To run IGMP snooping on a 3550 in L2 only IGMP snooping must be enabled on switch ports. However until IGMP is enabled on the VLAN interface (this is done by enabling PIM) snooping does not work. also the Cat6000 has an option of enabling a "querier" on the L2 switch itself in case there is no L3 device acting as a querier. This looks like the switch has to see IGMP query messages before it will populate the multicast cache. Is this correct?
The following link does hint at this but it actually states that "When the switch receives an IGMP join request, it creates an entry in its Layer 2 forwarding table for the VLAN on which the request was received". This suggests that a IGMP querier is not required to populate the cache, but when there is no querier it does not work.
When the switch receives an IGMP join request, it creates an entry in its Layer 2 forwarding table for the VLAN on which the request was received.
