Ive kept cardinals with my Angel fish and still do. They dont bother them and the Angels are a little over a year old now..
Only problem I had was when I first introduced the cardinals into the water. The angels thought they were food and bit a few of them and killed them. After that, no one bothered the cardinals and they have been very happy ever since. If you introduce them to the tank, maybe feed the Angels real good first.

and have your net handy to scare the Angels away from the cardinals. In a few minutes they do settle down. Just the initial meeting you have to be careful of.