Subs does have BDCP, it's just called NUPOC.
Its basically the same. You can be accepted to the program up to 30 months prior to graduation. You will be considered active duty military with no obligations (no uniform, drills, etc). Really, the only difference b/w BDCP and NUPOC is the signing bonus (15k initially, then 2k when you finish NNPS) and your pay rate is E-6 prior to commissioning.
The part about the calculus and physics requirements and the interview at NR are standard requirements for all those who want a Nuclear designator, whether they come from NUPOC, NROTC, or USNA.
As far as OCS goes, the difference b/w applying for a nuclear designator and anything else is you trade the ASTB for the NR interview. And kd5pbo is right. NR cares more about grades, so do well in your classes, especially technical classes, and ESPECIALLY calculus and physics.