... etc.About those health concerns - if you have no cuts or open soars in or near your mouth - swallowing isn't going to cause a health problem - those 'germs' cannot survive stomach acid and that happens before any chance of entering the bloodstream.
What lingers in your mouth, could be different, if you trust/know the guy well, probably ok. If a new guy and you're not sure I would practice the hygiene pointers mentioned already.
Also, if OP is asking this - It is one thing if it is on the menu - another thing to read how much she does it - like 2 or 3 times a session and you are next to kiss her? That's always been a little bit of a turn off to think about when kissing - that's why I try to see low volume providers - but that is no guarantee either, just better odds.
AND - Does CIM matter to your overall business? A little story - when I lived in FL, I saw a very popular provider who did not CIM but had a centerfold body and just seeing her naked all over me was worth the ticket - saw her often enough we became 'friends'. I would help her with some advertising, etc. One day she calls, 'What is going on? I'm getting dozens of requests!' I said, 'I haven't done anything, must be a great review.'
Sure enough, a guy did CIM with her and put it in the review. I told her and she freaked out - saying, 'he didn't make a sound or even tense up, he just went off and I didn't think I should stop.' So, it made a big difference. She added a Full GFE experience to her list of services with higher donation.