When you get your Pro hub, and start adding your Pico Remotes to it, do not associate (in the Lutron App) the Pico Remote with any Lutron Switches that are also paired to the Pro hub.
Instead, you install the Lutron Integrator App in Hubitat, and add your Pico remotes to Hubitat. This will then cause the Pico to show up as a Button Device. You can then use Pushed, Held, and Released button events to trigger actions within Hubitat Apps, like Button Controller and Rule Machine. Each of the 5 buttons can be used for whatever actions you like.
Following on what @ogiewon said above, you can use the raise lower buttons for most devices just as if they were tied to a Lutron dimmer, by using pressed/released with startLevelChange and StopLevelChange. There are posts here about that capability. @mike.maxwell got all of this working, and could chime in....
Okay, so the held function is like the native behavior the pico's have with the lutron hub, right? As you hold it down, it continues to dim (or brighten) until you release it. I ask only because most other button controllers use "held" as a long press (i.e. ST_anything).
There are two Pico drivers. One treats a Pico like a Minimote, and gives each button two functions: Pushed and Held (along with Released). The held timing can be set on the device page. The second driver, called Fast Pico, offers only Pushed and Released events. Both allow the raise/loser functionality.
The difference is that for the regular driver, the raise/lower functionality is started by the held action, and the actually raising/lowering begins after the held timing period. For the fast Pico it starts right away upon the Pushed action. In each case, it stops when the button is Released.
That's such a better way of handling a button! Finally! I always thought ST's way of doing it was odd with the pressed, double pressed, held thing.
And the buttons are numbers like this, right?
You would have to see their full product line of keypads to see the pattern it fits into -- it makes some sort of sense from some engineering perspective when looked at that way. For example, the top and bottom are on and off, 1 and 2. For a two button Pico they are still 1 and 2, etc... A four button pico lacks the center button, #5.
Well this is kind of a bummer. I have around 12 Caseta switches in my house paired to a non-pro bridge, and I just bought a bunch of RadioRa 2 equipment and a Hubitat for conditional logic, but I was hoping to leave my existing Caseta switches and have them work together with RadioRA 2, at least at first. But now I’m looking at having to buy the Caseta Pro Bridge if I want to have the two systems work together, but spending another $100 on a system I’m moving away from seems kind of dumb. I, for one, would appreciate Caseta support via cloud, even if it’s not as good as local control.
Welcome to Hubitat!
Unfortunately, Hubitat has made it VERY clear that cloud connection to Caseta is not in their game plan currently. And if you've ever tried the cloud integration on ST, you'd see why. It is PAINFULLY slow. While telnet locally is about as close to instant as you can get.
Are you technically inclined enough to set up Home Assistant? (You could even use Hass.io--both the components you'd need to integrate it with Hubitat, the Hubitat MQTT Brdige and an MQTT broker like Mosquitto, are available as add-ons.) If so, Home Assistant has some sort of non-Pro-Bridge integration for Caséta. I think it might still rely on the cloud (my understanding is that it basically pretends to be the mobile app, which I imagine hops through Lutron's servers, but I'm not sure if it still needs that after setup), and I'm not sure if Picos are among the devices supported, but if you're desperate, it's worth looking into.
Or you could buy a Caséta Pro Bridge for $97 new and sell your old one on eBay for hopefully not too much less, or maybe you'll find a used Pro on eBay for less as well. Obviously, this might not be a good idea if you're thinking about moving to Radio RA2. Your Picos will work but all your in-wall devices will need replaced, and you can occasionally great deals (I bought two and never paid more than $175 or so) on new or used RA2 Main Repeaters on eBay if you're patient. But you could also keep both and tie them together with Hubitat where needed. With how expensive RA2 switches and dimmers are, you might come out on top even needing an extra Pro Bridge on top.
Depending on your use case, it may be worth it to have a Caseta Pro bridge.
Potentially save some money, put the Caseta devices in out of the way places, use Hubitat to connect with any RadioRA 2 devices via scenes or keypad buttons.
Caseta Pro bridge is a good hub for adding Picos. a) if you are approaching the device limit on your RadioRA 2 main repeater(s), and/or b) If you are using Picos and Hubitat logic then there is a potential performance issue with slight delays of light response. The Picos are transmitters only and there can be communication delays as the path becomes Pico -> RadioRA 2 main repeater -> Hubitat -> RadioRA 2 main repeater -> RadioRA 2 dimmer. Putting the Picos on the Caseta bridge is one way of minimizing delays. (The better IMO is to program the scene in Lutron software to a phantom button and call the button in Hubitat.)
Is programming the scenes to phantom buttons to prevent popcorning of the lights?
Also, if I upgrade to the Caseta Pro Bridge, is it possible to have Toggle / Room Monitoring buttons on the RA 2 keypads monitor a room with Caseta switches (keypad button LED lights up when lights in Caseta room are on, and turns off once lights in that room are all off)? If so, would I accomplish this with phantom buttons, or would I create unactivated RA 2 switches in the RA 2 software wherever there’s a Caseta switch and then have Hubitat mirror any on / off events from the real Caseta switch to the unactivated “virtual” switch in RA 2?
Yes, the main repeater sends a single command and all lights programmed to it take their actions. As opposed to sending a different command from the Hubitat hub to each light.
I don't have many toggle buttons, and none with Caseta devices. I think you'd need to go the unactivated device route. I don't think a phantom button would work as there has to be a load somewhere in the scheme.
And note that normal scene button LEDs probably won't work as you would like, Caseta or not, if you are using a lot of conditional logic. For example, I have a scene button that sets lights to different levels based on the current mode. All but one of the levels are phantom button scenes. The button LED can only be tied to a single scene, so the LED is off for all but 1 mode.
You guys gotta talk slow for some of us simple humans. 
