Simultaneous dual-band routers have two APs (Access Points), not STAs (STA is a Station, i.e. client device).
APs of course support multiple associations. Clients support one association at a time.
In re-reading your original question, the answer is Yes. If you have two simultaneous dual-band routers that both support WDS, then you could form WDS links on both bands. I don't know, however, how traffic flow across the two links would be handled. There are no routers or APs I know of that do link aggregation of multiple WDS links.