I know that some of GC members tried Blender at least once. Here is a relatively new
Blender_addon/GIMP_plugin (released 2 mo ago)
allowing to paint 3D Blender objects in UV/image mode using GIMP. It's all being done in real time with both Blender and GIMP running.
I've been testing it over this weekend and it works quite well.
P.S. when you click on the link it will offer you attachment download - don't worry, nothing's going to download on your computer, it will simply open
addon manual in your browser window.
Here's the
video link