It sure is when a Domme lets her male sub wear a strapon and then uses the strapon to climax instead of her subbies equipment. So why couldn't it be a submissive thing?
But to answer the TS, I'd say that giving oral as a dominant is perfectly acceptable for teasing, rewarding or for the Dom(me)s own pleasure as many have already said here.
It doesn't mean that the Dom(me) can't demand his/her sub to give oral to them to get their pleasure out of using their sub.