I don't think anyone has ever questioned Dubose's defensive accumen. He's one of the more knowledgeable defensive coaches in the game.
His decision making, both on and off the field, is what left something to be desired. As head coach at UA, he completely mismanaged the offensive side of the football with the exception of the stretch during 1998 and 1999 when he gave Charlie Stubbs more control. And ironically enough, his defenses at UA during his head coaching tenure weren't really all that much to write home about. He was stubborn to a fault with his defensive scheming. I've read stories from former UA players about the Kentucky game in 1998, where Tim Couch fried our secondary because Dubose insisted on playing man-to-man coverage for the entire game. Said Dubose believed that you weren't tough if you couldn't play man-to-man. I remember Dubose's secondaries getting lit up on several other occassions.
At any rate, I wish him the best. The Memphis job is a very tall order. That program was moderately respectable for a period of time under Tommy West, but they've just utterly disintegrated.