Probably not. OSE is really just (in our opinion) the purest form of retro-clone out there. But, because this system has no added house rules, it's super adaptable to almost any basic D&D system out there. If you use any retro-clone, you should be able to use Worm Witch.
That being said, OSE is seriously awesome. I would strongly recommend you get the whole set as soon as you can.