I have added ATF to my fuel for years with no observed ill effects. This I HAVE observed... those who run it praise it for cleaning the injectors and improving the performance. Those who don't say it is bad for the motor and you should not use it. MOST of their information is based on what they have heard or read, not personal experience.
I would not be concerned about it harming the motor. I keep hearing how the friction modifiers are a problem, but the factory uses ATF to lubricate transmissions and transfer cases with no problems. I am convinced it will be fine there. The cat could be a different matter. Although I have no personal experience there, I CAN see how it could plug the converter.
Steve Keim