There is no such thing as cholov stam anymore (except Germany), it’s called akum or cholov treif, per Igros Moshe
Where in Igros Moshe?
Rab Belsky’s heter is not based on the established facts the Vets do to the cows.
Rav Belsky’s heter indeed seems weak, but others are mattir based on bittul (R’ Yecheskel Roth, and I believe that’s the basis on which R’ Dovid Feinstein is mattir as well.