Proximo (and I'm assuming Gladiator, as well) is *not* a unit frame addon. Grayhoof (Proximo's author) is adamant on that point. A mod moved his thread to the unit frames forum and he had them move it back.
An arena opponent frame mod is different from a unit frame mod in many ways.
edit: I would include Proximo and Gladiator in a pvp mods comparison instead.