I am in the middle of this very battle. There are some, though very, very few spray foams that you can use without the prescriptive ignition barrier when the air circulates to the common area, and then only when they are covered with an approved alternate thermal barrier. Most ES reports contain the restrictions already mentioned. What I have found is that those restrictions are the same criteria use in ACC 377, appendix X (acceptance criteria for spray foam) and the foams were tested under those criteria, therefore the ES reports must limit the use to those criteria. I have found at least one product that does not contain those restrictions but only when their intumescent thermal barrier is applied. That thermal barrier is a two step process, which must be installed in specific conditions which IMHO wouldn't be easy to accomplish or verify in a 2' crawlspace full of ducts and pipes.
So on the one hand prescriptive code requires circulating air from the crawl to the common area, and on the other hand prescriptive code prevents most foam plastics from being exposed in those crawls. For my part, I have been successful with a few builders in getting them to circulate the air properly and use insulation other than surface applied foam, I have been less successful getting my bosses to back me up on it.
It should be noted that I have spoken to several reps from the chemical corps that make these foams and they have provided (sometimes reluctantly) information and confirmation of my findings. I get the impression they realize there are some issues with prescriptive code compliance but that not enough inspectors have caught on to it yet for them to worry much about it. JUST MY IMPRESSION.