There was a case a while back where someone played like a thousand games or something against a low rated bot to incrementally raise his rating. They told him to stop already...
Pretty sure though that if you use common sense and play reasonably rated bots, it's fine. Of course eventually you need to figure out why playing against fellow humans is so stressful. I'm often wrong...
I have just recently discovered that you can play rated games against chess.com's live bots. I was a low 1200 2 days ago, but some 10min games against the live bots have now brought me to 1500... A part of me doesn't think it is fair to increase my ratings this way, but then again the bots' ratings come from real players. I do feel very stressed against real players, something I don't experience at all against bots. I now feel comfortable spending a long time on one move. Is it okay that I keep doing this?