Slave starting.
If the firewall mounted glow plug resistor is removed or bypassed. It is still ok to slave start the truck as long as the front battery has 12 volts or more. Basically, have at least one good battery of the two and make sure it is the front one. If both are bad, do the two civilian jumper cable thing to seperate power sources for each battery in the truck.
Remember, the truck is a 12 volt Chevy that has extra wires added for the slave system and the 24Volt starter. The slave system doesn't go directly to the batteries. It goes to the distribution strips on the passenger side firewall. The goal is getting 24 volts to the starter motor, not charging the truck up. Yes, the batteries are connected to it, but not individually. That means 24 volts could be back fed into the 12 volt side of the truck if the front battery is stone cold dead when the slave cables are hooked up. This can also happen on a truck with the glow plug resistor still there and functioning.
A DVOM should be in the truck at all times is my suggestion. If it won't start, check each battery. If the rear is dead, slave cable to another mv or civilian jumper cable just the rear since the front is good to go.
If the front is dead and the rear good. Swap them so the good one is in the front. Then slave away.
If they are both dead, Charge them individually or jump them individually until the gauge on the dash is in the yellow. Then, you can slave it without worry.
The original question of this thread was about white smoke and no start. His problem turned out to be glow plugs burned up by the resistor. If they had checked out good, another thing to check real fast is the green wire on the IP. It is the fast idle and cold advance power. That really makes a difference when starting a cold 6.2. If you doubt that, go unplug yours and try to start it cold. It might "harumph" just as you let go of the starter, but it probably won't run on its own. Throttle will have to be applied and held for a few minutes before it will idle too. Just something else to keep in mind if your truck ran yesterday just fine but won't light off today.