The same good be said about having a party with pizza at the same place. If they already are planning to offer something like that, I really don't see why they should care what he is wearing. It's a promotional event so it would be bad for them to treat someone like that badly.
I think some dressing is a lot less worse than someone actually making a party in a funeral home to begin with. That isn't really the place to do that, but they own it and if they think it is going to be good for them let them do it.