Actually, any band who performs using "screeching electric guitars - heavy percussion, and a squalling female vocalist" isn't performing music, regardless of which genre of music the song originated in.

I love a lot of rock music covers of traditional songs by a lot of musicians. The question is, as far as I'm concerned, not whether a rock band "should" cover a trad song, but whether they do it well and to my tastes. Which is how I judge any music performance or recording. Where the artist is born, whether they were first trained musically as traditional musicians, pop musicians, jazz musicians, or classical musicians, matters not one iota to me in grand scheme. Just matters if I like what they did with the music they attempt.