All WhatTunes needs is an "HTTP POST" (or GET) request with the right parameters (the whattunes readme covers that). It has literally been months since I did any major work on WhatTunes, so it should just work as expected. ;)
The plugin can be used to display album art via Amazon, if CG-Amazon is activated as well. I have to admit I've never even looked into what it takes/means to support iTMS links, but if someone points me in the right direction I'd be glad to look at it when I get some free cycles (heck, I might need to sign up as an iTMS affiliate, maybe can make a teensy bit back off the work! :) ).