There's a little-known halacha that an animal that has eaten nothing but non-kosher its entire life is itself non-kosher. (This is usually explained as a rabbinic prohibition because of how it looks.) One opinion in the Rishonim is this only had to do with animals brought as sacrifices (so irrelevant to our conversation); another is that it applies today, for any type of non-kosher animal feed; a third (which we apparently follow) is that the animal is rendered non-kosher only if its feed is so non-kosher that you can neither eat it nor derive benefit from it. See the Ramah and Shach on Yoreh Deah 60:1 (pdf).
אבל אם לא נתפטמה כל ימיה רק בדברים אסורים אסורה
But if it was fed exclusively its whole life only food prohibited from benefit, the animal is prohibited.
So if it's given this meat-and-milk formula as well as other things to eat, it would be permitted.
In the early 2000s the concern was raised that veal were being fed a formula that contained both meat and milk ingredients, cooked together. Rabbi JD Bleich's conclusion in a Tradition article (winter 2007) is that the way this meat-and-milk veal feed is made (among other factors) doesn't quite make it prohibited from benefit, only from eating, hence this problem would not apply; [the meat and milk in the formula weren't actually boiled directly together] however, he felt that if it took several paragraphs of nitty-gritty to explain why it's kosher, we shouldn't call it "glatt", which implies "it didn't take a great rabbi to figure out that this is kosher." There's also some discussion about whether they "finish" the animals with a few days of different feed, and again there's been talk whether they've redone the formula in general to something without meat or milk.