No. "One" does not express any reality added to "being" because it is manifest that the being of anything consists in undivision. For everything guards its unity as it guards its being.
To call a being "one" is not to express any extra reality about it. "One" is only a negation of division; for "one" means undivided "being".
By the way, Plato's mistake was to confuse the unity of being with the one of mathematics.