Well... the original Drumkit from Hell is a sample library that you use with Kontakt, Battery, or whatever. I think it comes as either .wav or Akai format. Toontrack were the folks (Swedish?) who created the sample library.
The second variation is Drumkit from Hell 2 which uses a proprietary version of the Native Instruments Kompakt ROMpler as a front end. The multisamples are all in a "locked down" .nik format so you can't use them outside of the bundled ROMpler.
The third variation is Drumkit from Hell (DFH) Superior and/or DFH Custom & Vintage. These both use a proprietary format, but with a unique front end.
IME the DFH2 had some real issues due to the fact that it was a joint venture between Toontrack, East-West and Native Instruments, and no one really stepped up to the plate when it came to customer service/technical support issues. YMMV.