Sorry for confusing broadcast with multicast. I don't have any expertise in the multicast area, but I think I understand that you're asking about LabVIEW support for IGMP and the overhead associated with maintaining a multicast port.
I figure you can probably do a Web search as well as I can, but I found a reference to someone's 1994 Ph.D. thesis on multicast-enabling a LabVIEW application:
http://www-itg.lbl.gov/~deba/ALS.DCEE/quarterly_rpts/q496.html
Maybe this is a lead for example code and updates on more recent work in the area.
Regards,
John Lum
National Instruments