This is kind of a silly question that comes up in vegan forums on a regular basis.
The short answer: yes, of course semen is vegan if it’s exchanged in a consensual manner.
I’ll give you a slightly longer answer if you’re interested in why.
Semen and The Definition of Veganism
Depending on who you ask, you’ll get a different definition of what being a vegan means.
But in general, you’ll hear something like:
The goal of veganism is to reduce the suffering you cause for others as much as possible.
This means abstaining from animal products like milk, which involve suffering for cows.
But semen (and I assume you’re only interested in human semen), can be given consensually without suffering.
No (sane) vegan would have a problem with it, so go nuts.