Hello Adam
I believe that the confusion here comes from the fact that you are using HSRP. So the SVIs on the switches are not acting simply to route traffic, but they are also acting as backup to each other.
When you have an HSRP arrangement, it would be helpful to take a look at HSRP-aware PIM. As this Cisco documentation describes:
Protocol Independent Multicast (PIM) has no inherent redundancy capabilities and its operation is completely independent of Hot Standby Router Protocol (HSRP) group states. As a result, IP multicast traffic is forwarded not necessarily by the same device as is elected by HSRP. The HSRP Aware PIM feature provides consistent IP multicast forwarding in a redundant network with virtual routing groups enabled.
Ideally, we want the multicast traffic to be forwarded by the HSRP active router for any particular VLAN. This allows PIM to leverage HSRP redundancy and avoid duplicate traffic. In this way, the DR is the same as the active router.
As for the RP, it is considered best practice to use Anycast RP, which allows for redundant RPs, which you can configure as the addresses of the SVIs themselves, rather than the virtual IP. Take a look at this Cisco Community thread for more info on this. For more info on Anycast RP configurations, take a look at the following lesson.
Now having said all of this, you haven’t told us what the behavior of your topology is. Is multicast working with your setup? What malfunctions or deficiencies do you see? Let us know how you get along!
I hope this has been helpful!
Laz