Cannot citizenship be revoked for past violations?

There are acceptable grounds for revocation of naturalization [1], but I'm not sure that having previously violated visa terms necessarily qualifies. The question becomes was he lawfully admitted to permanent residency, and was there a concealment of material facts or willful misrepresentation involved in the process. We would need to really see his immigration file and have knowledge of the dates he was in the US, and when he performed work.

[1] https://www.uscis.gov/policy-manual/volume-12-part-l-chapter...

Not really. It has only happened a couple times in hundreds of years and was about foreign spys