They are legally required to label these products “non-dairy”
Did you read that somewhere, or is that just an assumption? I’m pretty sure there are coffee creamers which do not say “non-dairy” on them.
If indeed this was a michshol (I don’t think it is, for a couple of reasons), although the OU couldn’t force a company to change their labels, they could refuse to certify.
I don’t see why they should, though.