I'd expect it to (eventually) have all duplicated files have one of the duplicates on the new drive, yes. Though I'd still recommend putting the Scanner balancer as highest priority.
You can plug a Storage Spaces array into a DrivePool pool as if the array were a normal drive, no problem.
It's trying to convert a Storage Spaces array back into separate drives that can't be done non-destructively (nor non-painfully, in my experience):