I have two modern bikes with cast wheels. Whenever I need a new tire I take the wheel to the dealer who fits a new tire and valve stem.
On some occasions, I've taken the wheel to another service shop that is not brand specific and they fit a new tire and valve stem - which I'm sure is not a brand specific part.
I've been doing this for 30 years and never had a problem, so to me, a valve stem is a valve stem.