Personally, I would assume not swallowing would have more to do with personal pereferences and the overall taste before I'd assume it was because they were vegan.

However, I don't think it would quite an issue. Unless, of course, the person is attempting to become pregnant, and thus the fluids would likely be seen as a waste.

That being said, I'm not a Vegan, or even a vegetarian... Hopefully someone who is will be able to help better.