Well a RTBS tank should be one of at least 30 gallons and prefferably heavily planted. If the only other animal in a tank of this description is a snail, I doubt the shark would pick on it. If the tank is over-croweded, too small or lacks hiding places, the shark most deffinately will start bothering the snail.
I've never heard of a 'white-tailed' shark. There are albino versions of the RTBS but they don't resemble anything I would call 'white tailed'...