I registered 2 cars in Maricopa County this week without having to pass emissions: a 1979 Porsche on Monday April 9, and a 1969 Camaro on Tuesday April 10.
I used the MVD location near Scottsdale and Bell. In both cases, when they asked me if I passed emissions, I said I was applying for the "collector car emissions exemption".
My cars are insured with Tamra at MK Insurance, a sponsor here on the site. I brought a copy of my insurance card and the completed insurance application on which I highlighted the policy's limitations (eg not primary car, not commuting car, parked in locked garage, 1000mi limit, etc). In both cases, the clerk went back to check with a supervisor and returned within a couple of minutes with my new plate.
The second time around, they gave me a bit of difficulty because I didn't have a "letter from the insurance company" -- perhaps Tamra could draft up a boilerplate as a benefit to her Arizona customers?