I think you will need to own that hub for the length of time you use the ST cloud. @ogiewon or @bertabcd1234 will know better.
I got a ST V2 hub on eBay for $35 just to integrate my SleepIQ bed as a contact sensor through the ST cloud. I have no intention to re-sell that hub.
You definitely need a SmartThings account (actually a Samsung account now), but I think you might also need a SmartThings "location," generally associated with a hub. I think the only way you might be able to get one is by registering an ST hub. I already have all of these things so can't say for sure the other way. 
As stated above, I do know you don't really need to keep the hub online for cloud-only features like this, though sometimes it seems happier (responds faster via Alexa and doesn't complain about unreachability are the only things I've noticed) if you do. HubConnect also wants your local ST hub IP address, even if it's not even online.
Thank you for the clarification - I've never had anything physical paired to ST, and the hub is boxed in my attic.
I forgot that I did give the V2 a static IP while setting up HubConnect. My perspective was that $35 to take a cloud integration off my Hubitat (and possibly other cloud integrations in the future) was worth it.
Thank you, I have an NVidia shield so I’m considering Samsung SmartThings Link for NVIDIA SHIELD | eBay
Also, I saw Homebridge on the first page. I’ll do some research myself but can you give me a jist of it? I use maker api, how is this better? My Homebridge devices will also show up in h.e?
Thank you
I'm not sure where Homebridge came into this picture, so you might need to explain more. Any Homebridge integration I know of exposes HE devices to Homebridge, not the other way around (think of it like the Alexa or Google Home integrations).
As for a hub: unless you find a really good deal, SmartThings seems to care a lot more about their "real" hubs than the shields/etc. That would be my preference if I were to actually use it. But I guess if you just need a random device to get an account, it won't matter much.
Hubconnect just includes an option to expose HE devices to Homebridge, the same as you've been able to do with standalone apps before. It is not related to the SmartThings integration; it's a different option. You also still need Homebridge, and it still doesn't get Homebridge devices into HE (nor does anything I'm aware of in any direct manner, virtual workarounds excepted).
A v2 or v3 hub is probably best, so good choice there. You can also use them for Zigbee device firmware updates if you ever need to (e.g., if you bought any original-firmware SmartThings Buttons, one of few firmware updates that have ever fixed anything), so it wouldn't be totally useless even though you could probably take it offline when you don't need it.
Thanks for your help
So, as a quick test... I just created a brand new Samsung Account for SmartThings using the New SmartThings App on my phone. No requirement to have a hub using that Mobile Phone App. This also created a default Location.
I then logged into the SmartThings Classic App on my phone using the same new Samsung Account (be sure to pick 'New User' when logging into the classic app, even though you already have an account - it's a SmartThings 'thing' !) I then went into the MarketPlace, Remotes and Buttons, and then picked 'Logitech Harmony Home Hub', which allowed me to log into my Logitech Account, select a Harmony Hub and corresponding Activities that then showed up in my SmartThings Account. I was able to activate and use these Activities within SmartThings without a hub.
The last step would be to get HubConnect working without a physical ST Hub... Perhaps @srwhite could explain if that is possible? I have not tried yet.
Wow thanks. It’d b cool not to have to buy one
I have setup hubconnect in order to access an integration through the ST cloud without my ST hub plugged in. I think I entered a random IP address since it required something.
I recently (Christmas time) tried to do some things with Samsung without a hub. I have an account, and I can even upload user code into the web portal, but I get stuck where it asks for the hub ID number. I don't know how to fix that. Everything I googled said a hub is required and there was not a workaround.
Thank you for this. I setup my V2 with the SmartThings Classic app (which needed a ST hub), and didn't realize I could have gotten around that entirely!
Well, I am not sure HubConnect can work without a ST Hub (i.e. cloud to cloud only)... I just went through the process of installing all of the ST Apps and Drivers in my 'new' ST account that does not have a hub. I am seeing an error from the Remote Client SmartApp which I believe is due to the fact that I do not have a ST hub connected to that account... sigh... 
I may dig out my O.G. SmartThings v1 hub just to see if that resolves the issue (which I bet it will...)
I just tried this as well. Same outcome. Here's the thing though. Once you setup HubConnect, then you can remove the ST hub.
You could be right, although my ST hub was unplugged long before I ever setup HubConnect, the hub and location existed in my ST account, so perhaps that was a necessary step.
Or maybe something has changed in more recent versions of HubConnect?
I think you've hit the nail on the head.
So, I dug out my very old ST v1 Hub and added it to my new ST account. Afterwards, I was able to get the HubConnect Remote Client SmartApp on ST to complete the initialize process without any errors. I then unplugged the ST v1 Hub and everything still works, as you've all mentioned above.
So, the question to @srwhite and/or @csteele is... Is there anyway to remove the dependency of having to have a ST Hub during the initial process of connecting the ST HubConnect Remote Client App to the Hubitat HubConnect Server App? Since ST no longer requires a physical to set up an account (using the new ST Connect Mobile App), it would be great to not require it during the setup of HubConnect.
EDIT: code snippets removed out of respect for @srwhite's comments below.
The Mac address check was originally done in preparation to support HubAction http calls as part of a hub "detection" scheme that was never fully implemented. Both SmartThings and Hubitat asked me to consider adding HubAction http support for hub-to-hub calls.. Obviously that hasn't quite found its way in to the code yet. 
I have concerns with removing the hub requirement. SmartThings might not look to kindly having their platform used to bridge their cloud integrations to a competitors hub while bypassing the rest of their ecosystem. It could also run afoul of their agreements with those partners. Having had ArloPilot blocked from the platform, I'm naturally concerned about treading lightly here since many people use HubConnect with SmartThings.
Understandable. With the caveat that their ecosystem now includes WiFi-only devices. This may be why the new app doesn't have a hub id requirement, whereas the Smartthings classic app does (or did at any rate).
For me, the choice to keep a ST hub was a no-brainer.
Download the Hubitat app
