Melvin Smith was strictly a vocalist who recorded for RCA and Groove in the 1950's, and then was part of The Nite Riders, a successful show band led by Doc Starks and featuring legendary pianist Van Walls, into the 1960's. I'm pretty sure that he's not the guy you're talking about.
Little Melvin (Underwood) was (is?) a blues/r&b vocalist/guitarist who recorded for small labels in Louisiana in the late 50's/early 60's. Around 2000 or so, he was based in Upstate N.Y., and played at the bar mitzvah of the son of a very good friend. I met him and he signed a copy of an Ace CD on which two previously unreleased tracks of his appear. I'll get in touch with my friend and see what he knows.