for reference ive allways had at least one common pleco with my rays and have never had a problem.
i have however lost several plecos that were housed with rays for several reasons and lost quite a few because the rays ate or tried to eat the plecos.
i currently have a vampire pleco and common pleco with my rays but have had others with no problems.
i also belleive the suck marks that the plecos are blamed for are commonly caused by other rays rather sucking on the rays discs (as i did myself but found out different when the same marks appeared when the pleco had been removed ) rather than the plecos that get the blame because of the "sucker mouth" name
).