No ... there is no evidence that mites have any ability to evolve to be resistant to OA .. unlike treatments based on thymol it is thought that OA works in a completely different way to kill the mites.
Have a read through this old thread:
http://www.beekeepingforum.co.uk/showthread.php?t=14938
There is no obvious way that mites could become resistant (certainly in the short term) to this type of physical acaricide - unlike Fluvalinate (the active ingredient in Apistan) which is effectively ~ in simple terms ~ is a poison that the mites ingest and which affects their nervous sytem .. like many poisons administered in small doses all species can learn to live with them and almost become immune to them in a relatively short time. One of the reasons that mites became resistance to Fluvalinate was that beekeepers unwittingly allowed the strips to stay in the hives, thus administering small sub lethal dosage over long periods - thus allowing the varroa to build up an immunity to the stuff.
I'm a non-treater but I recognise that this is a course of action that will not be accepted by everyone (if I were honest I would suggest that, in order to allow our bees to evolve we should all stop treatment and face the consequences) but in the absence of this my next best suggestion is for a massive move to OA by sublimation in the beekeeping world of the UK and a concerted effort to treat our bees simultaneously with a treatment that we know is exceptionally effective when used over three brood cycles.
If we are not all going to become non-treaters (and I think it unlikely) then from a pragmatic view our national plan for varroa should be to try to reduce the numbers of mites at a time when they are vulnerable. Indeed, I would suggest that our National Association should be at the forefront of a focused campaign to make this happen.
But what do I know ?