As I understand it, yes.
Is there some reason to assume it is impossible to draft a document that would meet state requirements? If not, assume that it does meet state requirements.
Why must we assume that it is in a state that does not allow MEWAs? Let's assume it is in a state that does allow them.
Your caveats are appreciated and noted. If it is a legal impossibility under any circumstances to have a multiple employer flex plan, please state so and let's move on. Otherwise, please assume the arrangement is valid.