I am not able at this time to test your assertion due to a lack of suitable test equipment, but I can tell you from past experience that I explicitly tested this feature, TX inhibit, on a trunked system, and found that it did NOT inhibit attempts at registration. However, the scenario was slightly different. The radio was not programmed using NAS scan. The test here was to see if TX inhibit prohibits registration when the radio is set to listen DIRECTLY to a trunked system, not doing it via a trunked member of a mode slaved scan list.
Under those circumstances, using a 1 meg IMBE Astro Saber as the test radio, it DEFINITELY tried to affiliate. But I can't tell you what level of firmware and DSP code was in the radio. All those things may be significant factors that affect the outcome when trying the same thing with another radio.
It was those experiments that directly led to me figuring out the non-affiliated scan method. Because TX inhibit alone was just not stopping the radio from affiliating.
Ever since then, I have STILL always been leery of TX inhibit. I have been suspicious that it doesn't ALWAYS keep the radio from transmitting without the user being aware of it.
Thinking further on it, attempting to trigger memories that are 20 years old, more or less, I do think you're right based on dimly remembered memories, plus the logic of TX inhibit in trunking being a feature that would depend on the radio actually being parked on the trunked system, instead of listening to it via scan while parked on a conventional channel.
I think that clarifies my experience. And forgive me for my imperfect memory of things long in the past.