It would depend a lot on the tile and what kind it is. In general most tile is going to be safe, but sometimes with things like granite you might find that oils have been soaked in as part of the polishing that can leach out. Had that issue once and learned the hard way. Actually added nasty oily film in the water I got the fish out and they ended up being fine. Maybe it would not have hurt them anyway, but it ruined the water and did not want to take chance with fish.
I would think with Stingrays one of main things you want to make sure is there are not sharp edges. Some tile can have very sharp edges that would not be good for fish, but especially stingrays.
Thanks i would definitely test them out first in my 10g see if the tile reacts with the water. I found that natural slate are pretty sharp i don't know if i should risk trying it.
I also want to know if anyone kept their rays on a tank with marble tiles?