Of course it wouldn't have stopped everything, but it would have helped - probably a lot. When everybody is getting their 3rd-party stamp of approval, those that do not are a lot more conspicuous.
Also, one of the steps in a typical IRB process is to sanity catch mistakes. As mentioned in another post, the people spraying bacteria over SF probably believe they were doing a "safe" experiment about dispersion properties. In an environment were it was regularly expected use an approval process, there might have been a chance for someone with biological knowledge to inform the experimenters of their error.
Also, one of the steps in a typical IRB process is to sanity catch mistakes. As mentioned in another post, the people spraying bacteria over SF probably believe they were doing a "safe" experiment about dispersion properties. In an environment were it was regularly expected use an approval process, there might have been a chance for someone with biological knowledge to inform the experimenters of their error.