hmm. interesting. I hadnt created a gimp brush as of yet. might just try to use the texture directly. it was built for photoshop at least CS1 and above.
I had to convert it with my ABR viewer. It does work in Gimp but only in black. It is not picking up color even though it's created in RGB mode. The pattern which was included in your zip file is not recognized by GIMP. If you did not create this pattern with Gimp, Gimp will not recognize it even if it has a .pat extension. The JPG however, does work. It can be placed in the Gimp Patterns folder and works beautifully. Nice work on that. Good job.