The engineering board probably won't have much to say about this. In my state, they weasel out of this sort of thing by claiming they only have authority to regulate licensed engineers, and no one else. In other words, they can fine engineers and suspend or revoke engineers' licenses, but they can't fine non-engineers or do anything else to them. All the board will do to non-engineers is issue a cease and desist letter. I think it would be up to the district attorney's office to decide whether or not to pursue anything further than that against a non-engineer because it is against the law to practice engineering without a license, and good luck with that unless it is something very high profile.
I imagine you could report it to the general contractors' licensing board if there is one in your state, and they should be able to discipline the GC, hopefully by revoking the license, not that that would actually stop him from building more houses. I'm sure this is a violation of their rules of conduct, or at least I hope it is.
I would certainly contact a lawyer about this. I imagine you would have a civil contract case against the offender.