The first thing to notice here is that the rim diameter of 32 Auto is smaller than that of 32 S&W Long (and the other rounds based on it, including 32 S&W, 32 H&R Magnum, and 327 Federal Magnum). Whether or not the extractor of a particular revolver is able to grab this rim can only be determined by trying it. Remember that the S&W Long is a true rimmed cartridge, while the 32 Auto is a semi-rimmed cartridge. They are classified this way for a reason. Some Ruger revolvers do shoot rimless cartridges, having extractors that are specially designed for this. However, most revolvers are not so designed, and getting reliable operation is something that may be questionable.
Secondly, note that the 32 Auto cartridge is much shorter than 32 S&W Long, and even shorter than the 32 H&R Magnum and 327 Federal Magnum. If one studies a modern revolver (meaning one made in the 20th Century or later), a ridge in each cylinder chamber can be noted. This is because in the days of modern, inside lubricated bullets, the bullet is smaller than the cartridge case. Referring to the diagrams I've attached, it should be easy to see that the entire bullet may come out of the case of a 32 Auto round chambered in a 32 S&W revolver before the bullet's full diameter encounters and seals this narrower part of the chamber, allowing gasses to exit around the bullet before the full diameter of it enters the narrow part of the revolver chamber (called the throat). This not only allows the escape of expanding gasses, but it also will affect accuracy, as a throated chamber is designed to receive the bullet in the throated section before it has exited the cartridge case. Proper chamber and throat dimensions enables the bullet to enter the throat fully aligned with the throat and subsequent barrel. A bullet entering the throat and barrel crooked will not be accurate.
I might add that Ruger, in those revolvers which do handle both rimmed and rimless cartridges, usually provides a separate cylinder that's properly throated for the shorter rimless round, such as the 45 Colt/45 Auto Blackhawk.
Thirdly, and most importantly note that the 32 Auto operates at a much higher pressure than 32 S&W Long, 20,000 psi versus 15,000 psi. This, in effect, makes 32 Auto the equivalent of a +P load. Is the revolver the 32 Auto is being fired in able to handle this pressure increase? Was it designed to handle this increase? Has it been tested to handle this increased pressure?
Now, there are always those people who offer the argument of, "I've done this for 30 years and never had a problem." Such an argument reminds me of those arguments that go along the line of "My grandpappy smoked cigarettes for 30 years and never got cancer, so i think it's safe for me to smoke."
This is not a very scientific way to approach the matter, is it? Well, people will do what they're going to do, and i know I can't stop them. i also know what I'd do, faced with a similar choice. As my Grandmother used to say, "A word to the wise is sufficient."
