I doubt a corp card limit has anything to do with it, this isn't a business product.
I've built an image library for a FTSE100 company. $499 per year for storage and access to a decent API would have looked pretty cheap to be honest.
I've seen nothing that says that's changed.
The actual TOS make no mention of whether you can have a business account or not. In face the best practices page specifically provides guidelines for businesses.
"This guide is intended to help organizations—such as businesses, groups and non-profits—get the most out of Flickr."