Yes, a simple Google query returns a few astronauts who were or are vegetarians:
From the answer to my previous question that you linked:
In the shuttle and post-shuttle era, with actual toilets available, astronauts have more options, and can pretty much ask for whatever they want for their pre-flight breakfast -- for example, lobster and baked potato -- but many stick to the steak-and-eggs tradition.
In this modern age of manned space flight, having convenient and working toilets means that crew members can enjoy any dietary requirements they might have, limited only by the olfactory tolerances of the companion crew members and NASA guidelines.
Foodstuff that might cause health issues (oysters, shellfish, allergies, etc.) or otherwise might affect the other crew members or equipment/mission might well be denied. However, that's a different question.