No need for WDS, if you're using a direct cable connection, just create the same security profiles on the 951 for each AP matching the 2011.
Now, how would I need to setup 951, to extend all 3 WiFi networks, so if someone connect to Virtual AP 1 on 951 it'd get IP from 2011 Virtual AP 1 DHCP Server and so on?
I guess you have several DHCP instances on the 2011, each running on top of a different bridge where each virtualAP or vlan interface is added, isn't it?
What you need to do is extending each L2 segment on the 951 and bridge with each L2 segment on the 2011.
You should create the same VirtualAPs, with same VLANs on the 951, then bridge them with the interface (on 951) facing 2011 ether5.
Then create vlan interfaces on 2011 ether5, adding them to the proper bridges on top of each DHCP server runs on.