No...not the block heater...the plenum heaters in the intake....Cummins version of glow plugs.
I guess you could try plugging the block heater in and see if it helps. But as I said, a Cummins should start pretty easy at 32*F WITHOUT the heaters coming on. If it doesn't, you have a fuel supply related problem. I'd get the pressure at the lift pump checked at the very least.
My '92 got hard to start a while back, and we traced it to a bad o-ring seal above the fuel filter/fuel heater plate. Air would get into the line overnight and it would take some cranking to get the old girl to start. Once air gets in there, the fuel will siphon back in the line. Check all your fuel banjo fittings....one could be loose.