ASCOM is for Mount control, some focuser's and dedicated (CCD) astro camera's...it's NOT for DSLR's. More on ASCOM here:
ASCOM - Standards for Astronomy
Canon and Nikon DSLR's can be controlled using Backyard EOS, or Backyard NIK
O'Telescope
Stark-Labs:
Home has software (Nebulosity) for some DSLR control (NO Pentax), Image processing, and guiding (PHD).
If you want to use your Pentax, you will have to either use the built in intervalometer, or the wired one as DeadJohn has suggested.
So, to answer your question, NO, Nebulosity will not control your Pentax, yet may be able to stack and register the files acquired by the Pentax (as DeadJohn points out).
Personally, I use Deep Sky Stacker
DeepSkyStacker - Free download and software reviews - CNET Download.com for stacking from Pentax & Canon files, and Photoshop CS6 for processing.