Aileron attach screws

[GAHorn]

To no one in particular:
So, imagine this if you will: A "stainless" screw (with or without a barrier nylon washer or paint) thru an aluminum cowling, with the threads holding against a spring-steel Tinnerman nut. How many dissimilar methals are involved?
If that screw is holding a non-structual part such as a cowling or inspection cover, and if that screw is commonly removed (presumeably allowing for it's inspection) for oil changes, inspections, and other regularly scheduled events, then is it's dissimilarity likely to be a problem? No.
But would that fastener be in good service in a hidden location holding items whose structural integrity was necessary for safety? Probably not. Cad-plated hardware is used in those applications for good reason, not only because the electrolytic corrosion risks are low, but also because when such corrosion does occur, it does so at such a low rate that the adjacent, critical parts are not likely to be damaged beyond use between inspection periods. (And in turn, is why pencil-whipped inspections are such a bad idea.)