As long as you aren't changing your grip in anticipation of successfully dealing with the Dummy rounds.
I often had to make sure the guys & gals I was checking with them kept up the same pace of fire for whatever drills we were doing, so they weren't just taking their time and focusing more on not flinching for each and every shot.
Quite often I may simply ask to inspect the gun, emptying the chamber, as if checking something (sights), and surreptitiously NOT rechamber a live round while "loading" the pistol, instructing the shooter to quickly take the seemingly loaded pistol and make some quick & accurate shot on the target on which we've been working. Virtually all of the time the shooters get to experience an anticipatory flinch sans the recoil of a live round firing.
Once they actually believe and accept it's happening, it's easier to try and resolve. Nobody ever really wants to believe it's
them throwing the rounds off POA, and would naturally rather blame it on the gun.
Dummy rounds are better, as then they can be loaded in various numbers within the usual duty belt load-out of 3 magazines. I just don't let the shooters load the mags, and usually turn away so they can't see how many Dummy rounds are being inserted into how many of the mags they're going to be using.
As a long time owner/shooter of Magnum revolvers, I had to come to my own realization that I was capable of flinching when shooting even low-recoiling 9mm's, In a way, learning not to flinch when expecting recoil and muzzle blast is sort of like learning not to jerk/flinch when startled by a loud noise or unexpected touch when not using a gun.
Training can help mitigate and resolve a lot of issues resulting from how we program the software between our ears.