I have a 3750 that's currently strictly layer 2 (it does have Advanced IP but it's not doing routing at the moment), it has 4 vlans on it, 3 of which carry data and 1 just for management. I also have this switch plugged into our core with a trunk, the trunk only carried the one vlan for management....the other 3 vlans only exist on this switch.
The servers that sit on this switch do most of their communication with multicast and currently I have IGMP snooping disabled, whenever I enabled it alot of servers stop receiving multicast traffic.
What's the best way of enabling igmp snooping in that scenario? Do I have to assign the SVI's IP addresses and enable routing for igmp snooping to work properly?
What I suspect is happening, you probably don't have an active IGMP Querier. Normally this function is provided by multicast routers, but many manageable switches can perform this function too. The 3750 has the command "ip igmp snooping querier" for this purpose, since it's disabled by default. This command does depend on having an IP address; using an SVI IP address is one of its options. See "Configuring the IGMP Snooping Querier" within http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swigmp.html#wp1089644 for more information.