Yes, indeed multicast traffic can be a big problem for a wireless install.
You will see this requirement when the customer specifies separate streams for viewing vs storage, and in any deployments with multiple command centers that need access to the same stream in real-time -- such as for special events, where you may have a field command center and multiple remote operations centers. Additionally, if there are analog cameras on the wireless IP network (via encoders) many of these streams present themselves to the wireless side as multicast, regardless of the actual end-user requirement.
For b/g for example, this automatically brings down the data rate from 54 Mbps to 6 Mbps, because of the way 802.11 protocol is set up to deal with multicast traffic. That's why the ability to handle multicast traffic effectively is such a key requirement for wireless video. Firetide handles this via encapsulation schemes embedded into our routing protocol. This comes up in at least 50% of our deployments, maybe even at a higher rate; and this is where many of wireless providers hit a roadblock.
To clarify, mesh is not a Wi-Fi access point based -- i.e. there's no client access over Wi-Fi provided. Only other mesh nodes can see the mesh nodes. Cameras plug into an Ethernet port on a mesh node, so you do need to provide power to the mesh node, which in turn can provide PoE to the camera. To provide client access (if desired) you can plug in an access point into a mesh node.
Back to multicast traffic, it's not an issue on a Firetide mesh.