There is always some risk but in this case the risk is not very high. Std's in general do not survive the conditions of the mouth very often. Getting an oral std is very rare. So, the choice would be yours on whether or not you allow ejaculation in your mouth.
Just to let you know, though, there is usually a little pre-ejaculation fluid that comes out during sexual activity. So if you are giving unprotected oral sex, you are still getting a little fluid in your mouth.
im no doctor but i would say yes