I contributed to cataclysm in a very small way. Take a look at the fish next time you decide to pop open cataclysm, I wrote their descriptions. They didn't have any description beyond "This is a salmon" before I got through with them. I also added lobsters and non-giant crayfish. I wanted to expand into a mod that allowed the capturing/farming of clams, but no one would tell me where to find the code for traps. The closest I got was rivet telling me to "check the github." So I said fuck it and gave up.
Ah, nice. And I assume Rivet meant to check the source code. It is a pain in the ass to sort through, but if you have a rough idea of what to look for it's easy to search in windows. Figuring out how to make sense of what you find is another thing entirely.
Then again, maybe I just got lucky back when my very first contribution entailed a minor source code edit to enable ember carriers to function. Granted, that swiftly proved unnecessary due to refillable lighters getting reworked into a more modular function.
EDIT: And to be honest, concerning the devs, The Almighty Granola Bar was generally the only one I had trouble working with. Rivet was generally nice, if a bit eccentric at times. Coolthulhu put with unparalleled amounts of "wat do" on my part.