It could be a backcross, it's just so hard to tell with all the diversity common to lepomis hybrids, at least for me. Lots of variables involved even within crosses that are definitively known, that influence appearance.
I will say that two years ago I happened to be at the right place and time to witness a male BRES in a courtship dance with a female BG. A few days later I saw the same fish guarding fry in his nest. I suppose a female RES could've visited the nest also, but either way it appeared to me that the MBRES had successfully spawned. I have no way of knowing if this union resulted in recruitment, but it's an interesting question.
