I am sure many people will have strong views about this that are different from mine, but I say you should work there if you want to.
WHy? Because by doing so you are in a position to reach more "meat eaters" and educate them on the realities of meat eating, and you are also in a position to dispel the myths about vegans (unhealthy, skinny, wimpy, etc). People that come in there will presumably be there because they are interested in health and fitness, and so you will have many opportunities to tell them your "secrets" to health and fitness and thereby promote an animal free lifestyle. In fact, not only do I think it isn't wrong for you to work there, I think it is a GOOD
When I was vegertarian, I used to work in a lot of bars that sold mostly meat dishes. Was I betraying the animals? NO. How not? Because every reasonable opportunity that I had I promoted vegetarianism to all these hard core meat eaters. IT would usually start by them asking me "Are the chicken wings any good here?". I, of course, would eagerly respond "I wouldn't know. I don't eat animals." Many conversations with these customers ensued about the health aspects, the cruelty aspects, etc. of eating animals. I am sure that I educated many people on topics that they would otherwise probably not have been educated on. IN fact, as Rob knows, I got fired from that job BECAUSE of my refusal withhold the fact that I was a vegetarian.
The owner wanted me to lie about that. AS if I would ever promote meat eating.
In short, I think we can reach more meat eaters by being around them whether that means being the bartender that they want to talk to while eating their chicken wings, or the supplement health guy whose advice they seek when they come in to buy supplements. So my opinion is that you can help animals more by working in a supplemental store that caters to not just vegans, but to ALL people including meat eaters.
Catch my drift?