I’m going to change my bulbs in the outdoor lamps on the house.
I want to group them as ‘OutdoorHouse’, but I also want each side of the house to be one group aswell.
I have done this with a test bulb, though it just belongs to two groups, I have not tested it.
The bulb shows up in both groups in Z2M.
But could there be any other drawbacks/problems
So I tested it remotly (at work now), it looks like it works, but not sure until I see the bulbs at home.
Fingers crossed! 
Depending on what you want the setup can be a bit tricky.
Like if you turn on the entire house and then turn off one side, then the house group might be set to off.
You can work around that as long as you think it over.
Something like that. I have bunch of motion sensors. First OutdoorHouse is turned on at 3% rather yellow. Then each side will be at 100% at some white/yellow level, and after that go down to same as when turned on.
I have not had the time to test it, but looking into HA from work, it looked like it was working the way I want!