Were you talking about multiples of the same species or multiple species of angels or both? I have seen someone who kept about five of the same dwarf angel in a 180g tank so it definitely can be done.

We have three angels in our 210g that we've had for a couple of years (or more) and they do not even notice one another. They are a coral beauty (dwarf), a flame (dwarf) and a bellus. I would think that in a 375g tank you could keep whatever you like. The coral beauty went in first and several months later the flame was added. For a week or two there was some hazing and giving chase by the coral beauty, but the flame angel found a spot to hide when she wanted and never seemed too concerned about it. Introducing the bellus was completely without incident.