This fall's into getting bit by an upgrade from 6.x to 8.x.
Under 6.x, there was an option to convert multi-cast to unicast's... and apparently that would allow multicasts to work without having L3 ip addresses associated with each vlan. (So, prior to our conversion to a MM/MD environment, this worked... without IGMP-Proxy or IGMP Snooping).
We have multiple vlan's that are passed to a core router... somewhere in the order of 70 vlan's if I remember correctly.
Without enabling IGMP-Proxy or snooping, the core router would actually see the multicast join request, but ultimately that would fail.
So I'm having to add IP addreses to each vlan so I can enable IGMP-Proxy... Which I think officially converts us to L3, though we're not actually routing any of the traffic in the controllers or on the MM....
Honestly this is kind of screwy, but it seems to work.
*shrug*