Not the same frame that is for sure... The geometry iin some characteristics is the same.. The most obvious difference is the look. The headtube is much larger on the aluxx giant frame, its reinforced at the headtube.
Also, it depends on what frame you are talking about.. The frames for the giant bikes have changed for the 2007 and newer models (maybe its the 2006 and newer) ... I think your friends 'new' rincon isn't exactly new.
If you are talking about an older rincon, then yes they are just about the same frame, its a pretty generic model.