You can use Filter Forge as a stand-alone program, as I'm sure you know. Once you have worked on your textures in Filter Forge, you can import the raster results into XDP.
I downloaded the trial version of P&GD11 to test it out. I use a very old version of Paintshop Pro (8) as my plugin folder and point Xara at that.
After working on a texture in FilterForge using P&GD11 (32 bit) and pressing apply, the texture reopens in Xara with no problems. I know that in the 64bit XDP 10 that it will crash using Filter Forge.
Bob.
EDIT: Apologies, you have to lock the bitmap effect before using the texture, or it will indeed crash...