An 8x2x2 is a very large tank for many people to accommodate in their house and jeffers is right many male rays of various species will be comfortable in there providing good husbandry techniques and adequate filtration is provided.However its not only a compatibilty issue when choosing tank mates for rays,Oscars for instance are big eaters so when they defecate create lots of waste which puts a huge strain on the biological filter leaving the whole system unstable,there simply isnt enough water volume in a tank of this size to cope with huge and sudden blasts of ammonia entering it,remember Stingrays once acclimatised have huge appetites,tanks of the size above are relatively small for such fish so shouldnt be over crowded......be happy to observe your ray or rays,these are truly unique fish which deserve respect.
When that 500 gal tank arrives then sure its nice to see a few different shapes drifting about,but choose tank mates carefully,its not just whether your choice of fish is going to attack the rays,ask yourself,can i get the food past the other occupants,if your having to throw twice as much food as you would like to in any one feed just so that the rays get some then at some point you could run into trouble...especially in smaller aquaria.