Hi @bruce.thornton,
Yes, you can configure the ip pim sparse-mode command on L3 interfaces (physical interfaces, sub-interfaces and L3 Port-Channels) and SVIs (interface vlans).
That is actually a requirement when you have Hosts sending the Multicast traffic or Hosts expecting to receive such Multicast traffic. In other words, when you have such Hosts on VlanX, you must have 'ip pim sparse-mode' under the SVI (interface vlanX).
The command is not available on L2 port-channels (including vPC) since these are L2 interfaces and PIM is a Layer 3 feature, this is expected.
As an additional comment, you can have your Nexus establishing Routing with other network devices over an SVI (L3) + vPC Port-Channel (L2), which is OK and supported nowadays for the Unicast traffic.
What you should not have is a PIM neighbor adjacency with other network devices in such scenario. In other words, your Nexus should not have a PIM neighbor adjacency using an SVI (L3) + vPC Port-Channel (L2) with a 3rd network device.
In such case, the Data Plane vPC loop prevention mechanism drops some of the Multicast flows depending on their hashing over the vPC Port-Channel.
As a conclusion about this last point, to form a PIM neighbor adjacency on the Nexus family of Switches with a 3rd device, use only L3 interfaces and not SVI (L3) + vPC Port-Channel (L2) for connectivity.
Cheers.
