Django is anything but an underrated guitarist. Within his chosen genre of music (jazz) he is revered by nearly all other guitar players. If anything he is overrated--sacrelige I know. After all, the guy did have a fairground sense of timing and was just a little too romantic in his playing at times. You never really hear about that from anyone, even though it is true.

It's not surprising that most people who play rock or metal don't mention Django---he's not a metal or rock player. He's not even really a blues player. And not only that, but his style really doesn't show in any metal or rock players. No one uses octaves like Django did, they use them more like Wes Montgomery did in the 60's. Similarly, no one phrases like Django in the rock genre.

So, great guitarist? Absolutely. One of the best? Without question. Relevance to rock/metal? Not much.

His influence in the jazz sphere is great, but not really much past that. He may be an inspiration, but not much beyond that at this point. That's why he's not mentioned often.