Are you planning on running unmodified vegitable oil or methylated/ethylated oil?
With unmodified oil you need a preheater on the tank to lower the viscosity of the oil to a point where it'll flow through your fuel system. Even then a lot of time you may need a two-tank system where you start on regular deisel then once everything is hot enough you flip over to the veggie oil.
The methylated/ethylated oil, which I believe is what the bulk biodiesel fuel sellers sell, can be run identically to regular diesel. It doesn't need any preheaters or the engine to be warmed up with regular diesel. However, this biodeisel is an INCREDIBLE engine cleaner. It'll loosen up and old deposits throughout your fuel line. Make sure you have a few spare fuel filters on hand.
All things considered, for something as critical as ambulances I'd stick with regular diesel. Biodiesel technology still has bugs that can shut a vehicle down for a few hours while simple repairs are made.
-Blast, who spent a summer helping a neighbor fiddle with biodiesel