Side-projects are a big debate. When does a band stop being one and starts being a full-time band? What's the difference between a solo career and a side-project, etc. Now, a side-project is a band started in parallel to another band. This is not the same thing as a band member leaving a band and forming a new one, or to join another band! For example, Soulfly is no more a side-project of Max Cavalera as Voivod is a side-project of Jason Newsted.
One might argue that a band can start as such but can stop being one if the main band splits-up. Or that while it's reasonable to have Wongraven or Chaostar, that a country band started by a Flotsam & Jetsam member would simply look out of place on a metal site. Our answer is that we have no choice but to go with a case by case approach. It might be a little arbitrary, but it's hard to define a rule that will apply for every case of a non-metal side-project. Yes, that might mean you'll have to ask us before submitting this guy's side-project. Usually there shouldn't be any problem, but if the side-project really has nothing to do with the heavy metal scene and/or would really look out of place here, chances are, it won't be accepted.