Yeah I think you can do this with a combination of the Alexa virtual device, the "Buttons to turn lights on/off" option in ML, and the "Enable override with dimmer level change" option in ML.
I don't think you would need all three and the most seamless option to me would be a button controller directing the Alexa virtual device and the override on dimmer level change option set. I think that button option is really meant for singular and one off buttons not really for button remotes like the hue.
Technically I have that override set in all of my rooms, but honestly I rarely if ever change the brightness level since I do per mode automation anyway. But IIRC the times that I have, and those were at the wall switch it did not override properly, but YMMV since I have wifi Kasa dimmers using the community driver. Also I think I may have digitally changed the brightness like once or twice and I think the override held in that occasion, so if you go down that route I'd be interested in your findings.
Honestly I feel like that Alexa option at the bottom needs a rebrand because it is much more useful than just voice commands, it's a virtual access to the devices in the context of the rule. Now you can get around this by adding the devices you are controlling to the switches that control the rule, a sort of feedback loop that HE stops after the first run, but this is another step and sometimes you don't want a single device to control the full group, e.g. not wanting undercabinet lights turning on overhead lights, but you likely would want the inverse.
Good idea to break this off to it's own discussion @cjkeenan , not directly related to the original post.
My use of this option is probably limited but the option is still something I want, to control my lighting outside of any (motion) automations I choose to set up. Aside from my (now) more common example of my Study where motion doesn't always represent presence in the room, another example could be use of my Exercise Bike on the Garage, though less common than occupancy of the Study
I'll test the Alexa option (hopefully) in the next few weeks and report back on my findings.
I think you might have set me on the right track, I've tested this in a spare bedroom and I think it is going to work for me. I'll test it in another part of the house before rolling out across the board, but so far I am very happy. I'll post back with my setup once I have finished. Thanks for suggesting this. And I agree, although it may have stared out as an Alex integration, that option does play a very different role for my setup and it would be worth renaming.
Finally got around to setting this up in two rooms, this is the original spare bedroom I setup. Now I just need to roll it out across the house...
Setup in Motion Lighting
You simply type a phrase into the Alexa or Google setting at the bottom of the screen, which results in an new device being created of type Alexa Dimmer with the same name as the phrase entered into the Motion Lighting app. Note, in this example the device is then used in the "Switch to disable on" setting and the "Disable turning lights off" setting.
This means if I turn them on with the Hue Dimmer motion lighting is suspended. When I then turn them off with the Hue Dimmer motion lighting is re-enabled.
Obviously this Alexa Dimmer device could be used in a number of different ways, including on dashboards or in additional rules.
Looking at it now, I should:
Add the override switch to the dim up and down buttons for the Hue Dimmer
Introduce a rule to turn this switch off when all the lights are turned off or turn the switch on when any of the lights are turned on by anything other than the motion lighting rule (not sure how I'll achieve this last one)