Well.....I would say that announcements of a tour featuring major metal bands is of interest and is fine at GMD. Announcing your unknown band's local show in a thread of its own isn't necessary, but I don't see an issue with things like this, basically the thread is here whether SMN News posts it or someone here at the forum posts it.
Edit: If every metal tour ever came and announced itself here, and was clogging the forum, I would see it differently, but this is specific, and of interest. People making threads promoting their bands is different.