Is it possible to kill a deer with a 410 slug?
Yes, it is.
It's also quite possible to wound one with it, given the poor accuracy of a shotgun shooting slugs, the feeble sectional density of a 410 slug and its low power level.
This is especially true when it is wielded by "visitors that might want to hunt but have not made the purchase of a gun.", in other words, raw beginners.
It's a bad idea.