ATF isn't an type of oil, it's hydrolic fluid

their chemical properties are so far apart.

As for if you add atf to oil, depends on how much you add in, if just a few drops, it may not matter too much, as engine high temp will vaporize it in combustion chamber; this is the same principle when coolant gets into oil due to cracked gasket. The more atf added, the more wear will result in to cylinders; at certain point, it will destroy your engine.