I have been told by a law enforcement officer, shop owner, and now a fellow enthusiast that if you do not fire in DAO that you are facing charges.
LEOs (particularly local police) tend to have a much much more limited knowledge about the law than most people think. This is not a put down it is just that their job does not require more than that and very few of them will have training to give them more than that. I never cease to be amazed at the BS I hear in gun shops.
Self defense is, in most cases, going to be a matter of state law. Laws and precedent vary state to state, but in most state you have requirements that are roughly similar and tend to be things like the following:
You are justified in using deadly force when you have an objectively reasonable belief that you are in imminent danger of death or serious bodily harm.
I suppose one could argue that cocking a hammer could be probative towards the issue of imminent but I do not see how it could reasonably be considered dispositive on that point or even very weighty. Now every bit of evidence that is put forth doesn't need to be a home run and in a case sometimes evidence that is far fetched might be proffered in the hope it might have some effect. Who knows what an individual juror might latch on to.
I would be more than astonished to learn of a per se rule in any jurisdiction that cocking a hammer prior to discharging a weapon precluded a claim of self defense.
As others have mentioned another way it could be an issue is in an argument that the gun accidentally discharged as opposed to it being fired deliberately in self defense.
What I would be much more worried about is whether the elements of self defense are clearly met or not. People in discussing cases that go to trial and may involve some of these details being presented to the jury like to focus in on the idea of one little thing swaying a jury while ignoring the big picture that the shooting in the first place was very questionable to even go to trial let alone get a conviction.
For example Fish shot a guy that was unarmed and it was far from clear that shooting was Fish's only recourse. Fish followed that up by making inconsistent statements to the police concerning what happened.
Fish also wasn't helped by errors committed by the court. Errors that eventually led to a reversal and remand. Charges have not been refiled (at least in part thanks to a substantive change to state law regarding burdens of proof inspired by the case).
Yes the prosecution made arguments related to his 10 mm and hollow point ammo but those were far from dispositive in how that case went down. Also from what information I've seen his counsel did a dismally poor job of refuting such absurd arguments, in short they simply didn't. Had Fish had a 9mm and not a 10 mm he still would have been in court and very likely still would have been convicted.