A couple of points to make here..
#1 You can treat with OAV ANY time of the year, even during other treatments, and supposedly (from what I have read) WITH supers on the hives, though I dont recommend treating with supers on. I always make sure all supers are removed when I treat.. by treating early spring and shortly after all supers are removed I dont have to worry about that.
#2 VSH Yes, you would have to buy queens every three years or so.. I buy resistant queens every year, and create new hives to test them.. YES, the genetics will become diluted as you raise new daughter queens... but consider, that you are also putting DRONES out there from these VSH/Survivor queens. Those drones are competing for the chance to mate any virgin queen, including those from neighbors and feral hives. Every VSH/Survivor Drone from that queen you bought that successfully mates "IS" helping raise the resistance of the bees in the neighborhood.. If YOU do this, if your neighbors do this, over time, you WILL add/build the resistance of all hives..
As far as I am concerned, it is the ultimate in irresponsibility to buy and keep generic queens, without trying to improve their resistance. You hurt your bees, your neighbors bees, and the feral bees. YOU TRASH any attempt your neighbors are making to have resistant bees.
When beekeepers begin demanding resistant queens, the breeders will either respond, or go out of business.
Having said that... What I have both seen, and read, is that you can develop perfectly resistant bees.. They survive in your locality with no help and no treatment..
Treatment = anything done to help reduce mite levels that is NOT initiated by the bees themselves.
Billy Joe can have great bees thriving with no treatments in Louisiana, then Carl buys six queens, and has them shipped to Montanna... Two years later all six hives are crashing from Varroa.. Difference in Climate? Difference in local mites? I dont know.. but the solution seems to be selection.. Make your own queens from the one queen you have that is doing the best against those mites.
Of those six hives, usually, one of them will seem nicer, healthier, and come through winter better.. Use her to make daughter queens... And of course.. Order a few more VSH queens from a different source.. Watch them all, over winter them, and next year, make more queens and order more queens..
If you dont want to be bothered making queens.. great, at least place a couple resistant queens each year. They are not that expensive, it keeps young queens in your hives, and helps prevent swarming.
As always.. this is my personal opinion.