I think its really unlikely they would ask for salary verification.
For CXO employees of publically traded firms and most government employees, its information easily found. If by executive level you mean Senior Vice President at ABC Petfood, you aren’t going to find it, and I’d be shocked it he’d give it to you. Asking would be a good way to turn an expensive and lengthy search processes into “hum, no, I don’t think I’ll work for you.”
I’m pretty sure I remember that in a discussion of this issue on the Headhunter blog someone said he got caught. But why lie? A company who was so hung up on previous salaries just might.