Unless they got a very good price for settling, I'm kinda surprised as well. I doubt they can or will counter sue if the criminal trial falls apart. Why on earth would you not drag feet until the criminal trial is settled, unless they want a very reasonable settlement.
In regards to the civil suit, both sides faced risks with waiting until the criminal trial to be concluded. If Mr. Zimmerman is found guilty, that could drive up the value of the civil suit and the HOA would have to pay more to settle it, since evidence of the criminal conduct of the HOA's agent, Mr. Zimmerman, could likely be introduced into evidence. If Mr. Zimmerman is found innocent, that could drive down the value of the civil suit, and the plaintiffs would have to take less to settle it, since evidence that the HOA's agent had been exonerated could likely be introduced into evidence.
I have faced similar situations in healthcare civil litigation in which a provider was being sued for malpractice and concurrently dealing with criminal charges arising out of the same course of action. A good example would be running a pill mill in which the provider was selling prescriptions. If a jury hearing the civil malpractice case of someone who died from an overdose learns that the doctor is doing 10 years at Club Fed for selling prescriptions, they are going to award a higher amount of money. You can try to keep out the conviction on the grounds that it would be prejudicial to the defendant, but that often does not work since it goes to impeachment by evidence of conviction of a crime. So I would usually try to settle those cases before the criminal trial.
So settling before the outcome of the criminal trial was prudent risk management for both sides. No matter the outcome of the criminal trial, the bargaining power of one side or the other would have been hurt. I suspect that the HOA was more worried than Mr. Martin's parents in terms of the outcome of the criminal case and was more eager to settle. Note that the HOA was only in the case as being vicariously liable for Mr. Zimmerman as being on duty for the HOA neighborhood watch, and that was sufficient to establish an agency relationship. I bet that HOA attorneys and risk managers all over the country are now going to be advising their clients to stop officially sponsoring or facilitating any sort of neighborhood watch program to eliminate this agency exposure.