Through research, I think I've found that the highest my minion's resistances can be in Hell is 50%, no matter how much "+% minion resistances" I stack. So, as far as I can tell I am at "max" minion resist, as I am getting +94% from my gear (I guess that's a little overkill).
That being said, Hell Diablo kills my minions with his pillar of fire ability in less than a second. My minions have between 16000 and 23000 life with all of my "+% minion life", which is at about +300%. (so I guess another question is, does the tooltip update with the accurate minion life as I add % minion life?)
Do I need to just stack a whole lot more minion life? They die in less than a second. How much minion life do I need?