Approximately how many bits of vermiculite were ingested? Any guess? (What is the proportion of vermiculite to coco fiber in your substrate mix?)
As noted in previous post- I don't think it's digestible. The problem is that it swells (absorbs moisture) so it could contribute to an intestinal blockage if very much was swallowed, but if very little was ingested, I doubt there will be any problem. I personally wouldn't use it for substrate for a snake, though it's useful in gardening & I used it for years to incubate snake eggs.
If your snake acts strangely though, or seems constipated, or you just want to pay for professional reassurance before you actually see any negative side effects, you can always consult your vet.
If you need to find one that's qualified with snakes, this may help: https://arav.site-ym.com/search/custom.asp?id=3661