Differing voltages with the same ground?
Isolation is unlikely to be required and several systems sharing the same 0V is very common and I would say typical. Problems can occur though and usually the problems are related to what is called "ground bounce". This might be a problem in a lightweight aircraft because you will want to keep weight down as much as possible. This might mean that you are intentionally keeping the weight down by NOT using thick cables for 0V wiring and NOT using star-point wiring for 0V. Star point wiring takes each sub-systems 0V directly back to the battery/generator to avoid currents in some sub systems causing ground-bounce on other sub systems.

So you ought to do tests to ensure you are OK but, my gut tells me that you should be able to make it work OK. The video signal max voltage will need to be checked to ensure it doesn't exceed 12 volts of course and this is easily fixed if it is.

Another problem is the regulator which I'm sure you are aware of - it's drop-out voltage isn't that great despite what their marketing boys say and on lean and mean wiring without decent star points this could cause a problem as possibly would the 36 volt max input to the regulator.