I feel like a lot of metal heads would like certain genres of rap that all happens to be pretty much underground now. They just need good recommendations.
what subgenres did u have in mind with this post
Any type of aggressive tongue twisting lyrical rap like Tech 9ine, Big Pun, or Pharoahe Monch; ultra violent dark shit like early LUM and various Southern subculture stuff - too much shit to list; underground lyrical West Coast trippy shit from the 90s like Hieroglyphics and Saafir; stoner rap from NYC at the same time that never seriously blew up like the BCC. Some of those guys are still active, some not - but I think metal heads are fine with that since they kinda have to have an appreciation for history.