You can cast teleport into a vehicle. If the vehicle is the enemy's tribe, your shaman will fall.

When you teleport, if the vehicle has at least 1 unit inside and has room for one more (at least), that vehicle will not be moving, so you can cast the teleport directly on it, and your shaman will be teleported inside.

Things change when you teleport into an abandoned boat or balloon: because it has no units inside, that vehicle will be slowly moving, so if you click directly, it might not always work. Because the teleport takes longer the further away your shaman stands from the teleporting point, the vehicle might have moved significantly, meaning you have to do the maths and aim it right - direct clicks on the vehicle and long  teleports dont match, and will most likely miss the target.

 

You can also teleport from a balloon into another, or into a boat, etc.

 

This video explains only the teleport into stopped boats (boats have units inside). Works with both boats and balloons.