Hi Leto,
I haven't work with RAP, but I believe that finally everything is translated to html markup processed by the browser on the client side. If my guess is correct, then TestComplete should be able to help you as it supports automation of web pages pretty well.
The best approach, as usual, is to try it yourself and check how the tool works with your application.
The TestComplete trial can be requested here: http://smartbear.com/products/qa-tools/automated-testing-tools (http://smartbear.com/products/qa-tools/automated-testing-tools/free-testcomplete-trial).
A lot of great videos can be found here: http://support.smartbear.com/screencasts/testcomplete/