Ugh..these topics are always pretty lame. You get a bunch of people..coming in and proclaiming that they know what metal..or rap..or country music really is. And then they list a bunch of obscure band names, thinking that they are the guru of their music genre. Its only a matter of time before someone claims that Blue Oyster Cult is metal.
GTA has had plenty of metal stations, sometimes they are mixed with rock. Will there be some less "mainstream" hits? Sure...but there are so many of these under the radar bands..that the chance for your fav...is pretty low.