DL would not entertain any claims for EU comp. for a domestic flight in the US. VS and SAS has nothing to do with any delay or cancellation of the DL flight.

The issue could also be that the DL ground staff at SEA will refuse to touch the ticket and ask you to contact SAS for rebooking the moment they realise that this is an award ticket issued by others than DL. This is a recipe for disaster in case your travel is disrupted in the US.