Im not sure about all these acronyms and verbiage you used but if you take the rent data against the zillow estimated value(which im assuming that is what zhvi stands for) in theory it would be good, but is entirely subjective based on the quality of the zillow estimate, which typically isnt very reliable. The calculation is really the actual rent vs actual market value or selling price of the properties. Zillow rent info is very reliable because thats currently whats being marketed and relatively what rent is going for. People dont screw around with rent listing prices as much as selling list prices, they typically want to rent the place asap. The estimates can vary by as much as 40% from true market value, depending on the city. In some cities with a lot of cookie cutter houses and sales info, the estimstes are probably more reliable. If you can get actual selling info in cities, it will greatly help your analysis, though zillow estimates are a decent starting point, maybe...
I also believe there are sites and other posts with the rent to value ratio already calculated for you. I realize the treasure hunt can be fun to try and find an untapped market, it just may be hard to get reliable data on your own.