No it will run fine with a mixture of propane and diesel. And for your education the first diesels ran off of coal dust.
I was aware of the coal-dust, but forgot thanks for the reminder.
However I still think the answer is an Omnivorous Engine.
I am going to go out on a limb here, watch the Wankel....
A great deal of research was done to make it Omnivorous and even throtte-less and has low pumping losses. Combine that with it's small size and power density, and you have a natural fit as a prime-mover engine for a Series Hybrid.
Go here for more research on the subject, it is amazing what was done not that long ago: