Working on the assumption that you want the vehicles to be combat ready during the same TW game you drop them in, VTOLs cannot carry them internally. Similarly, Total War is explicit in that mechanized infantry cannot be carried internally by anything smaller than a large support vehicle, small craft, or DropShip.
However, such units can be carried externally, essentially in slings and whatnot. You can land, drop the cargo, and off it goes. VTOLs with Lift Hoists are recommended, for the boost in cargo capabilities.
Note: you can fly while carrying such units, you can drop them off, but you cannot pick them up during the course of a game. You wanna do this, you have to start the game with the vehicle already loaded into the slings/nets/whatever, and once let loose, they're not getting picked up again. Plan accordingly.
