I don't think the SIAI has much experience writing code, or programming machine learning applications.

Eliezer's FAI team currently consists of 2 people: himself and Marcello Herreshoff. Whatever its probability of success, most would seem to come from actually recruiting enough high-powered folk for a team. Certainly he thinks so, thus his focus on Overcoming Bias and then the rationality book as a tool to recruit a credible team.

Superficially, that makes them less likley to know what they are doing, and more likely to make mistakes and screw up.

Sure, ceteris paribus, although coding errors seem less likely than architectural screwups to result in catastrophic harm rather than the AI not working.