Does insurance see it this way? I've had a couple precancerous moles (melanoma in situ) removed, which seems similar, and my health insurance provider billed me more than I was expecting because they didn't categorize it as preventive care.

I think so, even with shitty U.S. providers. I've never had a problem.

Most US insurance has very strict guidelines about what is diagnostic vs preventative for a colonoscopy. And its almost certianly diagnostic.