Depends on the size of the rays and pictus. I've got 3 hystrix rays @ 11", 7.5", and 6.5" along with 2 spotted pictus cats@ 3" and 1 four-lined pictus @ 5.5". They all get along fine. The spotted pictus are almost always on the go, while the four-lined sits under the driftwood most of the time. The cats have been in with the rays for about a year now, and there haven't been any issues. Quite often one or two of the rays will be under the driftwood and the cat will be resting on top of the ray.
What do you have for rays and how big are they? I probably wouldn't try this combo with bigger rays unless the cats were really big.