I ran a rag joint on my MTB it was a 36 spoke 14 gauge, no problems. My motor mount let go (my own negligence) and that ganked the chain pretty good and I have not been able to true the wheel since. I spent a week laid up because of it, so it was a pretty serious gank on the chain.
It was a Gary Fisher, so it was a decent mid level mountain bike. It was the engine mount that failed (again my fault), not the wheels. I weigh in at around 300 so I would think 36 spoke 14 gauge would be fine as long as they are connected to a decent hub and rim.