Maybe in Catholicism, but not in Scripture. Read the first chapter of Hebrews, in which angels are called ministering spirits, lower case s. Often they took the form of men, and were referred to as such, as in Genesis ch. 18, but that did not make them men. In fact, in the next chapter they were referred to as Angels.
In Genesis chapter 3, Satan took the form of a serpent, and the Bible refers to him there, as more crafty than any beast of the field which the LORD God had made. But, correct me if I’m wrong, nowhere does the Bible refer to angels, fallen or otherwise, as persons.
All orthodox Protestants would be on my side in this, because they believe in the Nicaea and the other early ecumenical councils, which depend on (the correct use of) this terminology.
Read the first chapter of Hebrews, in which angels are called ministering spirits, lower case s. Often they took the form of men, and were referred to as such, as in Genesis ch. 18, but that did not make them men.
You're not following what I'm saying, because you're equating "person" with "human being". All human beings are persons, but not all persons are human beings. The Holy Spirit is a Divine Person, but not a human being in any sense. Angels (fallen angels included) are beings of pure spirit. They are persons ("individual substances of a rational nature"), but not human and therefore not human persons. They are angelic persons.
But, correct me if I’m wrong, nowhere does the Bible refer to angels, fallen or otherwise, as persons.
It doesn't have to. Are angels rational by nature (i.e., intelligent, self-aware, etc.?). Yes they are. Are they individual substances, in the sense that one angel is not just a part of a bigger whole, but is an individual by himself? Yes they are. Then they meet the definition.