You can actually do this quite easily.
1. Make sure that the units you want to use are on the same side as your spawning units (Blufor side, Opfor side, Independent, etc.)
2. Go into the editor and select the vehicles you want to add to the spawning faction.
3. Go to the "ALiVE Virtual System" module and either a) leave it on "virtualize only sync units" then sync all vehicles to the module" OR b) switch the module to "virtualize all editor placed units" and it will automatically "take control" of all of the manually placed vehicles you put in the mission.
Remember that on option B if you DON'T want a certain vehicle to be virtualized, you'll need to sync it to the module (as the system would be virtualizing everything).
I do this all the time. I'll add in Helicopters, etc. and give them to a side.
As long as you have a BLUFOR, OPFOR, or IND AI commander, you're manually placed units will be controlled just as if they were spawned by the system.