I actually have two favourites. Symantec's Visual Cafe for Java and my second is the UNIX vi editor. When I am coding a GUI, then Visual Cafe is very useful, but when I'm coding non-visual objects, I like the purity of vi. I have recently obtained an evaluation edition of VisaJ, a GUI builder product that may well offer me all the GUI construction capabilities that I desire, and yet will work well with vi for the non-visual portions of code. This is a hard question for most corporate oriented programmers to answer because of the copyright and secrecy policies that most corporate employer have in place.
White papers are time consuming and non- trivial to write.
But, if your candidate has written any, then it is worth obtaining copies of them and discussing them in the interview. I certainly hope that these questions will work well for you. I have found them to be very helpful in technical interviewing. These questions help to separate the wheat from the chaff. If you have asked these questions and discussed them thoroughly with your prospective developer, then I trust that they will help you get a good feel for their level of competence and ability.