Typical reaction to shoot the messenger here. It's important to be honest with the OP, and I can see that some of you forgot to read the part where I said "depending on the circumstances of the NJP."
However any given CO might feel, the board is going to see it, and they're not likely to give that individual a pass.
If anyone here has first hand knowledge of someone who was selected for STA-21 with an NJP on their record, I'm all ears, but I'm doubtful that happens much, if ever.
I have known a couple officers who had NJP as enlisted it is rare for sure, the ones who said what happened all had similar stories, it was early in their career and it was something minor, minor to the point of knowing others that did something similar and just received counseling chit.
The one guy I did an application on who is now a Supply officer had an NJP in his first 6 months in the USN, served 4, went reserves, finished his last 2 years of college, then picked up for OCS.
I served with a SWO-N and when he was enlisted he was caught walking back on to base smelling of alcohol and was underage, NJP, finished NNPS, NPTU, fleet for a few years then STA-21. I said he was missing a star on his Good Conduct Ribbon, then he told me the story.
I think it is more common to find a LDO/CWO that early on had an NJP.
Then of course you have those that get caught doing something most go to NJP for that don't because the CO likes them, like the LDO ensign I know who was busted for DUI and never went to NJP, or the CO's cook who missed ships movement and never went to NJP.