You're right- the cam belt is usually the weakest part... unless it's got a chain or is gear-driven. I don't know the architecture of the motor at all. Lack of oil could certainly ruin bearings and perhaps grab the shaft. Breaking a camshaft (in, say, two parts) is an extreme case. Certainly in order to accomplish that other parts would suffer under the causal circumstances. There's really too little information to give a quality diagnosis.
I'm afraid that, if a cam could be sourced, the effort would wasted. Not only that, but could open up a "can of worms" with further repairs to other portions of the engine.

How difficult would it be to re-power the generator with an engine that is native to Belize? I mean, is there someone there with some fabrication skills and knowledge of diesels and/or generators?

OTOH, if the local diagnosis can be trusted, perhaps 'broken' has been mis-translated and a better term might be 'un-repairable'. If the people on site know that all they need is a cam, then the search for a cam should continue.

Hope it all works out ok!

edit:
wikipedia says the R2 was delivered in the Mazda Bongo, whatever that is.