One reason I know of that it could end up being prosecuted is because if he provides proof and it goes to court, any decent lawyer (in this case hers) will go after this evidence as hard as possible and that includes the person who gathered the evidence. There would be scrutiny, possible nobody would bother to prosecute but the evidence is gone, he's lost his "client"/boss his divorce case and opened himself up to a fine at best, a stalking/trespassing probation charge.

I've been licensed for a few years, I still don't do surveillance. It's not what I want to do and it's a minefield of problems. Also, hell, if you park somewhere long enough right now, you'll end up on Nextdoor within 10 minutes, every lady in the neighborhood will have you profiled complete with Ring pictures, license plate and possible known associates. The police will be with you shortly.