I'd like to know if it's possible to split a Cat6 port in an existing wall using a hub or router. The hub or router would then service 2 PoE IP cameras
Hubs are not compatible with PoE. A hub will not request power from the PoE-providing device, and it could not pass it on. You only want to use a router if you are connecting different networks because routers route between networks, even assuming the router provides PoE; many do not.
You can connect a PoE switch to the WAO (Work Area Outlet). The switch would provide PoE for the end-devices, and the switch would be transparent at layer-2 (unlike a router).