Re: one-two punch using Apivar and OA dribble?
There are confirmed reports of amitraz resistance but I do not have the source material. Rotating treatments is always a good idea, but combing two different treatments at the same time may not be such a good plan. Better would be to treat with the Apivar starting about now for your location, and doing a followup treatment with the OAD around the end of September or into October when the hive becomes broodless.
Thankfully, the bees are smarter than I am. They are doing well, in spite of my efforts to help them.