The Orontid dynasty was a powerful vassal dynasty, first of the Medians, later of the Persians, and then even under the Seleucids. Perhaps just their willingness to act under the umbrella of a larger empire was their recipe for success?
http://en.wikipedia.org/wiki/Orontid_dynasty
Yes, but it was relative success. The OP requires Armenia as a regional power, hard to achieve under someone else's imperial umbrella.