The scent-repellants probably only work for critters that breath with lung like structures. The mites that spread RRD only breath through their 'skin'. So unless the scent molecules hitch onto them and irritate them, it wouldn't happen soon enough.
I've had RRD on plants of many different sizes. The small ones that got it were often at the windward edge of a bed and where where the wind would break (and drop mites). The big plants make their own wind baffles and that's where the problem is.
In my other beds, if all the roses are about the same size, the winds slide over them (and so far seem to be dropping the mites on grass.)
I think there may also be a tie in to when the plants slow down at midsummer and the mites can't bite into undifferentiated growth/meristemic tissue. R. multiflora out in the wild seems to get sick really easily; R. setigera along the same fencelines is less susceptible but then setigera doesn't make the massive plants here.
THe problem is keeping wind moving and not having dead spots/ dead as in wind dropping to no wind spots within the roses.
In our species garden I haven't lost anything yet to RRD. (In a previous location a tenth of a mile away I lost two species to RRD; they were in better soil and on irrigation.) Maybe being dried out in the summer/fall has been a good thing for their longevity.

What repels these mites/what makes them move on/ is when they land on a surface and sense that it isn't a rose. Then they position themselves so the next puff of wind will move them on. This MAY be why some of the antitranspirants might work to prevent RRD. But this comes with no guarantees of any sort.

Speaking of sprays...has anyone here tried Quassia chips? It was used in the early 1900's to repel aphids, is totally natural and supposed to be a hundred times more bitter than quinine.