This guy has a pretty sick Max patch that he has for vocalizations. Check out Dehumanizer Here. Are there any max users that are able to pick that apart and possibly give some pointers as to how you can make that in reaktor? It looks like it has 4 pitch sliders and some spectral controls. It's hard to tell if the spectral fx are affecting the pitch sliders, or if they're just straight pitch. Even a screenshot of the patch would be cool. Enjoy to those that can use it!
I don't have time at the moment to download the patch, but looking at the video I think the "simple" implementation is using convolution where different "monster" impulse responses are chosen. The advanced engine then just adds additional processing. A bit of research of convolution should point you in the right direction.
BTW you can also create some good monster vocalisations with a vocoder and animal sounds.