I keep my 35cm motoros with FW needle-fish (10cm). I had a few eaten... but if you can take the risks, you CAN try~
What type of rays do you have?Well I have my 2 x 9" rays in with some rainbows which are around 3.5". They have been together around 6 months, the rainbows should eventually hit 6" and make a nice display in the tank. The rays pay the rainbows no attention at all. Not to say they wont eventually pick them off but they are doing well so far. The main difference is my rays wont get anywhere near the size of a motoro so you may get more problems when the rays get bigger.
I would go for it, accept the chance that they may get eaten and you might be pleasantly suprised !
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