Of course you wouldn't TEACH it (did I say that? I don't think so.) But don't try to change a guy if he's comfortable (and doing well.) Too many coaches try to put everyone in one "box." Grip and stance are the two most over-coached aspects of hitting (IMO.)
BTW- a lot depends on whether you're talking about the top or bottom hand- many power hitters grip with the top hand back in the palm but at the base of the fingers with the bottom hand.