It's a gamble. One atm I am taking w/ my retics and a hybrid cat and a TSN... the cats aren't big enough to eat them.... yet. I would start with the ray as big as possible and grow-out the cat until its to big to be covered by the ray then add it ( rays will eat smaller fish )... that's what I did and so far so good. But I do see in my future getting bigger rays or at least removing my m/f rays from the pool down the line. while the cats may be fine w/ the rays even once they could eat them.. I wouldn't think pups/birthing in the same tank would work... to many triggers for the cats not to eat the pups and possibly the female during the whole process, and once most fish start learning they can eat certain types of tank-mates... they do.
keeping anything w/ big cats is a gamble, anyone who tells you different has been lucky and nieve. catfish are predatory and opportunistic.