If you upload something that wasn't made in any way with RW Software we just ask you don't upload it because it would be misleading our members about what the Software is capable of performing.
Well, you can use other programs. The gallery started as an exclusive RW showroom, but it has grown since that time and you can upload icons and cursors via a web interface (I'll have to update the text on the library pages). It is just recommended that you mention what program you have used in the description of the sets or individual icons/cursors.