I'm not an SDI instructor, but I believe that Nitrox doesn't count towards ASDDP. That is certainly how the sentence would have been written, if not for that first comma which doesn't belong in the sentence for any grammatical reason.
"Complete four SDI Specialty Diver courses or equivalent; only 1 course without dives[-],[/-] may be credited towards the SDI Advanced Diver development program, with the exception of SDI Computer Nitrox"
I suspect you are correct. But, even without the comma that sentence would still leave some room for questioning the exact meaning. It just needs to be re-written to make it very clear, if Computer Nitrox doesn't count as a specialty towards anything. I assume it doesn't count as a specialty towards even the Advanced Adventure Diver, either...?
Hopefully, Jon from SDI/TDI/ERDI or an actual SDI instructor will come along and give me a For Sure answer.