It's also contrary to the ideals of a free market, if that matters to anyone.
I'll admit that it's ethical if one's ethical framework is based on Pirates of the Caribbean. "Take what you can, give nothing back." Which probably is pretty common, especially among people who succeed at business.
With many of these roles, it’s unclear who has the advantage: the seed-stage start-up or the key employee.
It's literally their job as a business owner, and millions of people successfully do this every year.
If that's the case where you're incorporated and operating, specialists in what the law says and how it applies exists. Use some of that VC money to use them.
That said, your examples are pretty terrible. ADA rules for buildings are incredibly clear, and a halfway decent contractor will know them. Ditto fire rules. Seriously, a business owner with a shed that hurts or kills somebody for not being compliant with fire codes deserves their day in court.
Oh, and the usual "Ignorance of the law is no excuse to break the law" applies here too.
Can you clarify what you mean by "ethical" in this case? It's not obvious to me which ethic / whose interests deserve priority in a case like this.