I don't get why this is funny, if they are killing the rabbits to control population then go ahead and use the dead bodies, but they shouldn't just kill them for fuel.
I think food would be a better use, but, have you ever tasted wild bunny? It's either really good or really gamey depending on the age and how much adrenaline was dumped into the bunny's system before it assumed room temperature. Bunnies for food works better when they are farm grown.
Now, as far as fuel, processing rabbit is no different than processing corn or algae. Every living thing contains fatty acid methyl esters and that is what is processed for bio fuel.
I would think you would be proud of them for reducing their carbon footprint by using a bio fuel.