I still dunno about that. I mean, if Marietta was the only reference to Riviera, sure I'd just think it was a cameo appearance or something, but YU is freaking FILLED with stuff from Riviera, so it's hard to say that.
And the Archangel's whole inclusion as an Accursed is a plot hole, like Sturm points out in that thread. (Wow, I actually agreed with Sturm! Is that a flying pig I just saw over there?)
I vote we hunt down the Sting staff who decided to put her in and make them tell us what the deal is. (That way I can torture them for things that made me mad like
» Click to show Spoiler - click again to hide... «
having to choose between Roswell and Rosary, killing off Gulcasa, killing off Ledah in Riviera, et cetera
and you can get a crack at them for things that made you mad too, like banner subtitles and stuff that they let Atlus kill in translation.) 'Cause that's the only way to really know for sure.