Yeah you cannot deliberately hit units in combat or your own units. Of course there is a bit of a loophole there if there is another unit in between, you choose to target them, and it overshoots into the unit in combat, that is allowed. Honestly, I found the thought of that a bit beardy so I pretty much don't point the salamander where there is a chance it will end up on a unit in combat. The thing is powerful enough as is.