You have to look at the word Saint. It means holy. So, every human who has died in a state of grace and is now in heaven is obviously a saint because they are in fact holy, but you also have to say the same of the angels that didn’t fall. You have to be holy to be in the presence of God, therefore we can and do call angels Saint or Sanctus which simply means “Holy” Gabriel, Michael, Raphael, etc. So, yes, every angel that is IN heaven would be called Saint.
If I am wrong in any way, I’m sure one of you will correct me.