I am working on an answer for that because Stutter Edit is on my wishlist too.
Now, you probably know that it will work with Apple Logic.
However the question for GarageBand 11 is: Will Stutter Edit be able to send MIDI to Garageband Effects?
Yes, you can send MIDI info to Garageband's Instruments, but sending MIDI to its AU Effects could be an entirely different matter.
I will try to get back to you.
Until then, Has anyone (reading this post) used Stutter Edit with Garageband 11?
Please, FACTS ONLY.