>alot of the time it says "I got permission to cover said song from said producer"
I've seen a lot of utattemita in my life, and I have never seen a video claim such a thing unless it was a non-vocaloid song, and even those rarely have a declaration like that.
You may be encountering a common mistranslation of the humble form of "to sing", which can also mean "was allowed to sing", but other than that, I have no idea what you're talking about.
Covers of songs with publicly available instrumental tracks are absolutely legal, and some more-well-known producers such as HoneyWorks even have notices on their communities in reaction to some well-meaning utaite: "You need not ask permission to cover our songs."