@Carl **********
just so you and your thai missus is clear. The immigration officer AT immigration buildings are NOT passport control officers at entry points to the country. They have abso-tively, posi-lutely NO clue about what you'd be asked entering on an O-A visa when you fly in.
Right now there's not enough consistency with the few reports we've had. Some people entering on their first entry with their O-A weren't asked for proof of insurance, BUT some were.
Some people stamping in on entries after their first entry were asked and when they couldn't provide proof of holding insurance from one of the 12 thai companies that offer it were stamped in on a 30 day visa exempt entry, told to GET insurance, come back to the airport and get the stamp changed to a year entry.
Good Luck, and definitely let us know how it works out for you stamping, in.
BUT
I can tell you with near 100% accuracy an immigration office in a tiny province with maybe a handful of foreigners on O-A visas IF that, isn't the place to ask about how it's gonna work when you stamp into the country at the airport.