Would the service department know this or should I assume they don't?
The Porsche Dealer should be aware of the 'N' designation and should only stock 'N' designated tires. If they are getting the tire from Tire Rack and a lot of dealers do (you can check to see what you should pay for the tire before shipping and handling by going to www.tirerack.com, they get a cheaper rate than what is published) they will also know what to put on your car. I don't work for Tire Rack, but they are pretty knowledgable.
Elvis Has Left The Building, can you smell the tire smoke???!!!....
2008 911 Carrera S Cab (Meteor Grey)
2007 Porsche Cayman S (Basalt Black) - Sold
2006 Porsche Cayman S (Midnight Blue) - Sold
2004 BMW M3 (Grey) - Sold