Diplomatic visas are only issued to diplomats traveling to a country on a diplomatic mission. I don't even know if they're issue them into a regular passport. There's not a lot of information because the lay person doesn't apply for them.
What is your wife's profession, and what is her purpose of traveling?
Diplomats should go through their contact at their respective embassy. But to answer your question, there is no residency requirement for the Non-OF visa, only the STV, METV, and Non-OA visa.
The law requires proof of onward travel within the time you'd be stamped in for. Immigration almost never cares, but the airlines will. Airlines are fined and responsible to return someone to their home country at their cost if someone is refused entry, so they will (more often than not) deny you boarding without proof of onward travel.
As for your visa, you're entering on a 30 day visa exempt entry. Thailand pass has nothing to do with your visa status.