To find an example of this, all one has to do is sample Marilyn Manson's music. He's a psycho-freak who is perverted every sense of the word. He's not decent in anyway and his music is degrading to women and to his fans. Yet somehow he literally had a cult following during his most popular times in the mid-1990s. Manson's act is one of the most horrendous spectacles on the planet when it comes to music and his style is certainly incompatible with being religious. Anyone who claims to be a "good person" and listens to Manson's music is either hypocritical or needs psychological help.
There is no way one can say that music is not religious to another individual. What we personally believe and feel through music cannot be taken away. Similarly, those who express themselves through writing and performing music can have many different backgrounds and muses. Who is to say that religion does not play a part in music production and enjoyment.
I do not think that death metal is incapable of being religious because death metal is just how they make the sound and how they use their vocals. It does not mean the lyrics have to hateful or angry or anything else. They can use the instruments and loud vocals and be religious with it.
I do not believe black or death metal music is incompatible with being religious. People chose to follow religion in a variety of different ways, but overall I do not think their chosen forms of entertainment should effect their ability to be religious. Music is created for entertainment purposes, there are many genres and people generally like certain genres for no known reason.
Music and types of music are not inherently evil. I know that a lot of black and death metal gets a really bad rap for being detrimental to society, but this is simply not the case. However, lyrics can be inherently something that is morally wrong. If the lyrics are bad, then it's not good.