If the pleco is well fed and has plenty of hide spots, you may be ok but either way, its a gamble. If the ray is 10" or so, I wouldn't be too worried. I have kept bushy nose, sail fin and common plecos with mine. Several of the plecos lost their heads...literally.
Hungry carnivore plecos may damage stingray by sucking stingray's back. Especially in small tank because rays cannot hide.
I keep many 8"-20" L190, L191 in stingray breeding pond. None of damages from each others. They live together perfectly.