As the patch is one year old, I've got no time to reintegrate the patch and the engine itself is a quite isolated part of commons math library, I decided to publish it separately on google code hosting licensed under Apache License 2.0: http://code.google.com/p/montecarlo-java/
There are few task left for the engine to be complete from my internal point of view:
1. Remove colt dependency and substitute it with commons math matrix functionality.
2. Make a coverage-guided unit-testing. Commonly used functionality is tested in the internal product but whole the functionality has not been properly tested yet.
3. Documentation clean-up.
I would like to see this library integrated back into Commons Math some days but it is not of my priority right now.