They won't care / it won't matter. The ONLY grades and test scores the Navy cares about are Navy tests and classes. Just remember - when you sign the papers, they own you. The only thing you have to negotiate with (you) just became theirs, so make your deal and get it in writing up front... If you want to go into electronics AND go to nuke school, make them put it in a contract. Something they don't emphisis is that if you do fail out / don't make it through Nuke school and prototype (which happens to more folks than do make it), they still own you and you get to be whatever else you went to school for (mechanic, electrician, electronics tech) without the nuclear part instead, for the duration of your tour. Oh, and nuke school is a bit tricky. Imagine 3 years of college crammed into 6 months. We went from 2 + 2 to trig & calc in 3 weeks. Then it started getting hard.... I didn't sleep on Tuesdays or Thursdays for the duration, and I aced the NFQT.
Anyway, it isn't a cake walk, but is definately interesting. My dad told me that the Navy Recruiter was the lyingest SOB that I would ever meet... He was right. In spite of that, while I was in I visited 14 countries, made 5 major cruises (North Atlantic, 2 to the Med, & 2 Caribbean), and when my tour was over, I got out and quadrupled my salary. Looking back (I got out in 1987), it was definately worth it.
Good Luck!