No Difference after removing the entire netfilter stack from the kernel.
I looked around on the vserver mailing lists, and I saw some people talking about problems with multicast, but I didnt’ get a feel for whether it was an old problem, or existing problem, or a fixed problem or if there were workarounds or what.
I saw one post that made it look like it might be possible to get one vserver working with multicast to a particular address, but I wasn’t sure. :/
Might be that the proxy mdns thing is the best answer.