If you two hosts are in the same cluster, DRS is enabled, and the vCloud Agent is on both hosts then either can be used for VM creation and placement. That said if a host is not under contention it could (and many times will be) used to start new vms, even with an empty host around. I have a feeling that when 11 was re-added to the cluster the vCloud Agent was not added to the host (hosts tab in Administrator - prepare host).
Now to answer the direct questions.. or at least attempt 
1. When a host is added to a cluster it will have the same resource pools as the cluster (resource pools are a cluster level construct)
2. Yes. When you create a provider VDC you supply it what resource pool it will be assigned to. Org VDC's are given a provider VDC as the base, so if you have multiple providers against the same vcenter (or other vcenters) then you can create a model where on a single vcenter, or single cluster you have many resource pools.
3. See #2.