Probably not, as we develop only for use on Linux workstations. We'd heard problems in the past with Windows/multiprocessing, and since we didn't have the time/machines to investigate, we just defaulted to false for Windows. Anyone could debug and send a patch to fix.
However, there's no reason you couldn't parallelize the gjslint calls themselves. xargs on UNIX can do this with xargs
To lint all .js files, one could do, in UNIX:
find . | grep \.js$ | xargs -P 0 path/to/gjslint.py
There is likely an equivalent in Windows, or one could be scripted.