“They hold chalav yisrael as a chumra, not as an ikkar hallacha.”
Nobody, not Rav Moshe ztzvk”l, nor any other posek who permits, under certain specific circumstances, the use of “cholov company (the term Rav Moshe ztzvk”l uses), holds cholov stam is ikar halachah and cholov Yisroel is a chumra. Nobody. The din of cholov Yisroel is brought in the Gemora and is clearly codified in the Shulchan Aruch. And just like any other davar ha’assur it should assur keilim. That is indeed how many poskim hold. Others are lenient in this regard and view cholov companies as mutar. But by definition one who uses only cholov Yisroel products is following ikar halachah even if cholov company (cholov stam) is also permitted.