depends how big the aro is and the gt also the rays, also how aggressive is th gt.....some say dont put overly aggressive cichlids with rays as the cichlid will bully them.
i say go for it but watch closely for a while because the cichlids could nibble at the rays eyes and if the cichlids are too small they can get eaten by rhe arow
Mono Sebaes are brackish water fish. Leave them out. If your looking at Motoro's, Teacup's?, Pearl's etc, Go with the cheapest, as you dont want a $500 ray having its eeys gouged out by a silly GT.