1. just install it for the primary; you really should have 1 domain with others directing to it for better results in engines (duplicate anything brings one down in points).
2. Yes, the script itself is completely separate from the UBB, as it only relies on standard data in the db it should be compatible with just about any install within v7.
Sweet
Point taken on the redirects - i've just moved a load of stuff over from another hosting company and registrar so things are a little disorganized at the moment. Ultimately everything will be redirected to a single point.
