Pretty sure there's places doing it, but I haven't really worked anywhere that used a Vanilla framework, except for the first few months, or have used an app that just uses something off the shelf.
I'm in the YC startup space, though, but have seen this also in enterprise.
Are they though? My impression is that most companies are just using frameworks or sdks that promise some degree of cross platform uniformity, and that’s why they don’t use the native toolkits. The savings come from not having to develop UI for multiple OS targets.