According to this question, both μ's and Aquors are real life groups.
So, I am wondering what other groups that are mentioned in Love Live! School Idol Project and Love Live! Sunshine!! are also based off real life idol groups.
In Japan, they are generally called as seiyuu unit (Japanese Wikipedia) when a music/acting unit (group) consists of voice actors. For a special case where a group also works as a real-life idol, it is called seiyuu idol unit.
According to the Wikipedia, there are 3 units, but only 2 are seiyuu idol units: