DaasYochid:
1: Regarding the CY point, by the OU putting their mark on the product, they are taking responsibility that the milk used (which presumably also has a Hechsher) is also not adulterated. The only issue is the Gezairah of Cholov Yisroel, and on that specific issue the supervision of the FDA (however that is done, I’m not an expert) and resulting fines is sufficient according to Rav Moshe’s Hetter. As for the Nirbater Rov’s teshuva, do you really believe that at the time of Rav Moshe the FDA came down to every single dairy to check?
2: Regarding the Treifus issue, Rav Moshe holds of a combination of the Chazon Ish’s terutzim (Chazal Koveh and evolution), but also holds that the Simanei Tarfus were only set for animals. For people, Tarfus only depends on Mekomo V’shaito if they can live (and brings a Rambam to prove it). L’cheorah, it makes for tremendous Nafkei Mina l’gabei the Dinim of Gozez/Treifah, Eidus, etc. I also don’t see why there should be a Chiluk between people and animals lgabei this din, and ask the Olam for their ideas.