Honestly, I don't really care unless Tarn cares. Plus, his opinion is the only one that really matters in this situation, but I don't really see the big deal. Although now that I think about it, they do seem to credit the song/sample to their "talented sound director" when nearly all of it isn't original. I like references to DF, but if they didn't ask permission, I could see the issue.
Even if Toady, Threetoe and Scamps all agree that is is ok for FRG to use the DF theme music, it just will not be the same as if SoR had a theme to call it's own. It is sad when a game aspires to do nothing more then mimic another, and has no desire to build itself a soul. While there would be no real problem, it sure wouldn't be a credit to the game, and the developers should be aspiring to more than that.
Anyway, DF is a grim and gritty game, that deals with the struggles of every day life on a community level. It sells itself on having more depth than all music composed since the turn of the millennia combined. You can not win, so matter what you do, and almost sarcastically, the catch phrase is 'Loosing is fun'. DF is meant to be some what of a sombre affair, and the music reflects this beautifully. SoR, however, I think would be a lot better if it choose a more light hearted approach, and sold itself as a game where you build might towers, dig vast dungeons and kick some goblin ass. The sort of game where as you do not win not because one day you loose, but because the winning keeps coming. The visual style so far looks to reflect this a lot more than the choice of music, and even some of the enemies seem to be hand picked to bring forth a sense of nostalgia for your 8bit childhood. SoR should feel light and happy for maximum impact, and the music would do well to reflect this.