Mark, the most powerful bombs in the US non-nuclear arsenal are "hyperbaric" bombs, aka "fuel air" bombs. Based on a finely atomized spray of diesel fuel. And then there's ANFO, a favorite of terrorists, also built on diesel fuel.
So while blowers are not required in diesel systems, and diesel is damned reluctant to explode, it can and does make a nice fine explosion if you have a high pressure leak spraying finely atomized diesel fuel in just the wrong way. Some folks say a blower should be used with diesel anyway, just in case.
A blower also will help to cool down a diesel engine after you shut it down, which will also help cool down the whole boat faster on a hot summer afternoon, and help keep the oil in the engine from cooking after shut-down.
So, not necessary, but not entirely wasted either.