Just want to make sure. Can you shoot at a character in a unit with a minus to hit (or is it special rule just for oxyatl-and empire[i think])? Also, new to the boards, hope to start contributing, great site
First of all, welcome to the forum! No, in most cases you cannot target a character in a unit. On its own next to the unit, yes. A couple of empire things can, there is an engineer sniper rifle and cannons can be directed to go through a specific model, but then he gets a look out sir roll. And of course it is a special rule for Oxyotl because he has better aim.
Actually you can target a hero if has Unit Strength 5 or more. Also if he is in a unit if the unit contains less that 5 rank and file models the hits are randomized and he can be hit that way, but if the unit is bigger he can't be hit at all. Look at pg. 74 in the rule book for more on this.