I have been playing around with WDS under OpenWrt approach, and notice the following:
a devices can not be at the same time a master WDS for a group of devices and be a station to join a WDS group (same frequency, different ssid and wep key).
It will depend on the chip and driver involved. AP(WDS) and STA(WDS) should be the same rules as regular AP and STA modes. In most cases you can have one STA and one or more APs. However, the APs will not come up unless and until the STA has connected to its AP.