ZSLHF. My initial info about the 737 Classic simulator landing on one AP came from a very senior Boeing instructor from the Boeing company. I assumed that it would apply to the real aircraft too, otherwise no point in bringing the subject up. On one autopilot (sim, again) the flare and throttle reduction is exactly the same as a two AP operation. In the sim I work with you cannot pick the difference between two or one AP autoland.
My initial post stated that there was no backtrim applied at any time. I was wrong. It does back trim just at the flare -whereas a two AP approach trims back at 400 ft.
If you think your particular Classic sim does not replicate a hard landing, you want to try the sim I work on. It fair rattles your teeth with the impact and as I have done more than my fair share of let us say firm landings in the real thing, I can tell you that our sim at least is very much the same as the real thing. When I see a late flare in the offing, I brace myself in the sim for a hard touchdown.
On the other hand I have flown 737 sims where the techs have deliberately adjusted the machine to do only soft greaser landings regardless of high sink rate at impact. Very satisfying of course but useless. I believe that is to minimise jarring of the machine and thus maintenance costs. Whoever does the fidelity checks on those sims must look the other way because no way is that a accurate replication of a hard landing.