That isn't true for all tents with one opening. The ones shaped like a dome have loot in them but the loot is usually clipped in the ground so you need to have your inventory window open to see it. The rectangular tents that were present in the DayZ mod that used to have loot in them, don't seem to spawn loot often if at all in the stand alone game.

:S This problem was fixed in the past and not its back :S