Yes, the nomination form will be the way to add relationships that aren't already in the tagset. I don't have it all set up yet - I'll get that done in the next day or two, and it will come pre-populated with a list of relationships.

If you'd like, you can list out the ones you know you're going to want in a comment here, and I'll make sure they're in. Of course, there will be opportunity to add more later as well!