I don't know about disguise. It's hard to tell from TV. But he has mentioned in an interview that he practices hitting kick serve off his slice serve etc.
The thing is, he doesn't really need all that great disguise. Except a few players, most players will have hard time returning his serve even though they know where it's going.
In terms of variety, he has it all. He has got a great slice serve on deuce, seems to hit slider 2nd serve rather than kick serve on deuce. He can flatten it out down the middle, kick it out wide.
Mark P, Goran I, and Sampras are somwhat similar servers. I feel like they have less margin of error than Roddick does. It semes like Roddick is able to hit harder with a lot more spin.
But when it comes to accuracy, disguise, I think Pete Sampras is the one. He could disguise it so well, and had real pin point accuracy.