I know that any VAT registered garage can service your car and as long as they use genuine parts your warranty is valid, in theory. I'm not sure how co-oprative they would be in the event of a larger claim.
Also unless you sell your car to another enthusiast they will not understand that Awesome will do a better job, they will just want to see VW stamps in the service book.
So what I tend to do is get the basic service done at VW, to get the stamp, and then have any other work that I can't do myself done at good old Awesome
Just my opinion of course