Are you strictly dating vegans? Maybe you are open to dating vegetarians? Maybe you view it as a personal choice and you don’t mind dating non-vegans?
Does the goal of the relationship change your answer? If it is a long-term relationship, or a short-term one, or a casual one, or friends-with-benifitis or even a one-night-stand?
It wouldn’t be a hard requirement for me for dating, but they’d need to have empathy and willingness to discuss veganism. Long term id expect them to become vegan, not because of me but because they came to know and believe in the vegan philosophy. I just don’t think i could be with someone long term who doesn’t value all life the same way as me.