Is it ok to leave cakes in the freezer without wrapping them in plastic wrap or foil if it is just for a few hours? Like maybe 3-4 hours? Will they not be as moist? Thank you!

If it's not frosted I would wrap it to keep it from drying out.  Not such a problem if frosted,   doz

true -- and the item can also pick up any smells floating about in the freezer too 

I agree with both, at least crumb coat before freezing and be sure there is nothing with a strong odor sharing the freezer.  It will be fine.