I had one male and three female MM in a 300G set up. I introduced 4 juvenile RTGG that were approximately 5". They coexisted very well for about 6 months. I came home from work one afternoon to feed my all my fish and noticed that two of my rays had blood in there eyes. I refrained from feeding, checked all my water parameters and everything was perfect. At that point I sat back and observed for about 45 minutes and sure enough two of the gouramis began harassing the rays and biting them in their eyes. I separated the Gouramis into another tank and my two rays recovered but one was blinded in both eyes. The blind ray survived just fine and actually had pups two years later.
I would be very cautious because I do know some hobbyists that have been successful in keeping the two species togetherI think the trick is to get gouramis that are older or semi adults.
I hope this helps.