Sure. With someone I'm involved with long-term. Basically, each of us flipping each other between oral/anal.
And not as a standard practice. But sometimes, the heat is strong and you just go with what feels right.
If you mean giving oral to a guy who had it in a third-person's ass, no.
Edited to add: "Safe" is completely up to you and what you're comfortable with. If you don't want to or don't like it, don't do it. Nothing wrong with that. Sex should be mutually pleasurable - not one-sided.