Yes, both Warp Stabilizer and the 3D Camera Tracker run as separate, external processes that send their results back to the main After Effects application when they're done.
Details here:
memory and storage tips for Warp Stabilizer and 3D Camera Tracker
Regarding the speed improvements: You say that you've noticed a 3x speedup. We've found that the speedup varies a lot depending on the characteristics of the footage being processed, so I wouldn't count on it being 3x in all cases. I think that our marketing materials ended up saying that the speedup was ~80% (so nearly a 2x speedup) across all of our various tests.