I suppose vegetarians should never become in need of a food handout. They might become offended if someone offered them an animal protein.
Homeless, and going to a shelter for food? If they don't like the menu because of their faith then perhaps their faith can get them a job so they are'nt homeless. Screw em', find another shelter!
If they've served pork soup in the past, and it's only become an issue of late with new homeless muslims, then no, it's not unethical.
If someone decided, knowingly, that if they added pork soup to the menu, and hadn't served it prior, the muslims wouldn't eat it, then it's unethical.
Need more explaination?
Is it unethical to serve pork? not at all, if someone does not like the menu they can go elsewhere. And the original question had nothing to with motive, simply provoked the thought of it being handed out to feed the hungry as unethical, and again that is up to the person to choose when seeking a hand out.