Well, we know the prosecution in this case is dumber than dirt so they may just open that line up for examination by accident because no way any prosecutor is going to serve that one up unless they make a huge error. Biggest thing going for Z in this case is his injuries. If he can get that in properly, the self defense defense wins. If they don’t get it in effectively, not so good.
I think this is why they are not using the stand your ground defense. The state has evidence to show that Z was keeping tabs on Saint Treyvon. So, to use that defense could hurt their case of self defense because the state will throw up the image of a guy following St Treyvon because he was black in a SYGD. No way the state can show or prove that Treyvon was threatened by Z causing St Trevon to confront him physically; Z had a legal right to keep him in eye sight; Z is a neighborhood watch guy and lastly he was doing his volunteer job. St Trevyon reacted beyond legal bounds and Z was defending himself, case closed. All IMHO.
In an immunity hearing, defense goes first, has the burden of production, and the burden of proof is preponderance of the evidence, more likely than not the use of force was justified. Nelson has all sorts of hooks she can deny that on. Not reasonably in fear of serious injury being a big one. Or she'd pull a Serino and say Zimmerman could have waited another 30 seconds (using her immense powers of hindsight). I wouldn't trust her with my dog.
In a trial, the state goes first, and has to prove the crime beyond a reasonable doubt, and has to disprove self defense beyond a reasonable doubt. Worst case is hung jury. I give that about a 15% chance as a racist is allowed into the jury. 85% chance of acquittal.
If he gets a sane jury. A juror whose mind is clouded by Liberal Mind Fog might have a hard time imagining that someone (TM) could attack another person (GZ) so violently without provocation, and thus regard the severity of the attack as proof that GZ must have done something to provoke TM. That's why some aspects of the TM character evidence are so important. To show that even if it's hard to imagine someone who would attack another person so savagely for no reason, Trayvon Martin was, in fact, just such a person.