let suppose u have a three router all of them currently running ospf routing , each neighbor of ospf send a hello message on the multicast address 184.108.40.206
ospf process once enabled listen to the link local mcast address associated with the it, as you specified.
same as in the case of eigrp or ripv2, but on different mcast addresses.
It's not a good idea telling these are multicast neighbors just because they listen to it.
A true multicast neighbor is formed with PIM/MOSPF or DVMRP running between the routers or interfaces to be specific.
1. enable ip multicast-routing on any two directly connected routers and ip pim sparse-mode/dense-mode between the two directly connected interfaces.
2. debug ip pim
3. do a sh ip pim neighbor to verify the same.