I notice my MP9 has more movement when the hammer falls in dry fire vs. some other pistols I have, 1911, 5906.  I noticed the striker is big in this pistol.

I have the apex sear and a trigger stop, so it's not the trigger.

Does the striker cause more movement than a hammer?  Can that affect accuracy?

yes it can.

For what we do, I would say it does not make a significant difference. Much more important is the speed of manipulation; a single-action trigger can be activated way faster than a DAO trigger. This can be especially significant with movers/swingers etc. A 1911 or CZ trigger is definitely more shootable, but weigh that against the extra hazard of abandonment... many top shooters take the trouble to completely unload their 1911s to avoid the chance of a DQ if the safety swipes off during abandonment. Thus unloading costs significant time.

If it matters, I switched from an STI 2011 to an M&P9 Pro for exactly this reason.