If you are selling a service using the theme then I think it is just fine as long as you are not reselling it.
On the legal FAQ as quoted below, the theme cannot be resold or distributed under any circumstances.
http://appthemes.com/support/faq/
No. None of our themes may be resold or redistributed under any circumstances. This includes modifying the design and/or adding new features then attempting to resell it as your own product. Also, since this is digital media there are no refunds once your purchase has been made.
Anyway, I will refer this thread to the developer for clarification.