I am a PRO user at Cognito Forms. And I also wanted this feature.
White labeling is possible for the Forms.
In fact they have a special embed feature that puts the forms 'inline',
not an iframe, so it really is a nice solution.
(*it also has iframe if you want that)
Notifications via email currently show
firstname.lastname@example.org so not exactly white label when you get a notification sent to your customer.
If you don't plan on sending your customer anything (like an email confirmation of any sort) then yes it acts like white-label very well.
But, if you reply to your customer via their email response system (Mandrill) they are required currently to add
email@example.com in the display name, making it obvious that you are using Cognito Forms.