No it is not. It is not a drug, but is classified as a medical food. Still, products are not required to be FDA approved to be covered by insurance, but many insurance plans use that as a guideline. The first tier is usually the insurance company's formulary. Then there is the non-formulary items that require coding or a physician's statement of medical need. But, generally, these need to be FDA approved. Plus, gray area items like medical foods usually have strict diagnoses that must be documented before there is approval. Once I was prescribed an elemental diet while awaiting my colectomy. I was denied coverage for it because it was only approved for coverage if you had a Crohn's diagnosis. I wound up having to pay a lot out of pocket for 3 weeks worth of prescription diet.
Bottom line is that insurance companies only do what they are required to do, and even then sometimes you have to twist their arm.
Still, it is not as if VSL#3 has a high rate of success, so it is kind of understandable. I doubt your GI could prove that it was better than anything else. It just has a few studies, where the others don't.
If you had no other options (like you were allergic to all the antibiotics), it might be worth pursuing. If it were me, I'd let it go and save your energy for a fight you can win.
http://www.vsl3.com/hcp/faq.aspJan