Eh?

The trains accept passes but some of their staff can be a bit unsure. First class passes are valid only in Comfort class - not in First. They operate between Munich and Wien and are an excellent alternative to the railjets. They use modern double deck sets so sit upstairs for the best views. Catering from self service machines so no restaurant card. They seem to be able to make up time if delayed because they have tremendous acceleration compared to the railjets. 

As far as I was aware on Westbahn Interrail is only valid in 2nd class, no matter what pass you have.