Is it harmful if a man performs oral on a woman with a yeast infection? Could he get thrush

No. Studies do, however suggest that application of saliva to the vulvovaginal area may "disrupt the balance" of candida to other resident organisms and immune components, predisposing you to candidal/yeast infections. Any risk for you or your partner may also be related to your immune system.
Yes. This is entirely possible. I would suggest waiting until the infection has resolved.
Possibly. Candida is an opportunistic pathogen in the mouth, usually rearing it's ugly head after antibiotics have altered the natural flora which usually keeps it in check. In theory, if a man had some decrease in his regular immune status, or was on antibiotic therapy, it could happen. Try using a douche made of plain yogurt and warm water several hours before sex if possible- it may help kill off yeast.

Related Questions

Are the chances high for a man to develop thrush after giving oral sex to a woman with a yeast infection??

May be or may not... Exposing to yeasts may not contract it or to develop its related infection, depending upon personal defense ability. In reality, you just have to wait, watch, and see how the things may evolve since this is a part of life, attesting that life is a constantly adjusting, changing dynamic process of struggle to cope with reality, certainty, & uncertainty of daily living... Read more...
Very low chance. Thrush in a woman usually develops because of an underlying issue in the woman - if she has been on antibiotics or has a predisposition to vaginal yeast infection. It would be unlikely for a man to get oral thrush by cunilingus unless he too had a reason for getting it like immunosuppression or otherwise but then again it would be most unlikely to transmit it this way. Read more...