Never having rays and not paying much attention to them, I've only heard of one problem reported by Jeff Rapps when his rays got chewed up by a vulture catfish.
In general vultures are a safe gamble but a gamble nevertheless, my impression is...
Are they called "Vultures" for a good reason? I only know what I saw of them on "River Monsters". Chewing on Rays?? Perhaps they are too stupid to realize they are not dead, or dying, just lazy and hiding? Your guess is as good as mine
They are called vulture because they are an ultimate scavenger with a unique dentition that allows them to take bites of flesh out of animals, dead or alive.
That's why many fear to home them with other fish. But IME, this fear is 99.9% unfounded based on the empirical observations by fish keeping community.
Vultures have another telling nickname "machete catfish".