Re: Using Hero System for Zombie Survival Horror
The first issue can be resolved (or at least partially resolved) by giving the zombies a Complication to the effect that they are always "out of combat" for DCV purposes. That would put them at half DCV for all attacks, and halve the penalty for called shots. A head shot would still be -4, but that's a lot easier to deal with than -8.
For the second, I would build the zombie bite with "must follow grab", giving the characters at least one extra phase to take out the zombie when they're about to be bitten. Making the bite do minimal damage would help, as leather jackets, boots, and gloves become viable armor, and you could even limit the bite by saying it only penetrates heavy cloth (like denim) on an 11- check. Human teeth aren't really the best for chomping through anything tougher than slightly unripe fruit.