Q u o t e: The "Mastery" skills aren't synergies, they are passives. A synergy comes as a secondary effect of a skill... like how FireBolt gives you an active skill, but also provides a passive boost (synergy) with FireBall...
I think it would depend how you define "synergy." I could see someone arguing that any skill that benefits another skill is a synergy, which would make many passives synergies.
Diablo 3 DotA: http://forums.battle.net/thread.html?topicId=16101821339&sid=3000