I'm under hte impression that base rock is always dead rock...like the stuff they have at hirocks.com
Live rock is a general term that covers gulf rock, keyes rock, tonga, fiji...etc...any actual 'live' rock, pulled wet from the ocean/aquaculturing pools, and kept alive during transport. Liverocks.com is great for live rock. I've heard good things about hirocks.com but haven't personally used them.
The only thing about using a small percentage of live rock is that you MUST be extra patient, and stock slowly enough for the dead rock to become live...which is really about the same average time as cycling a new tank: 4 weeks. Coralline algae will take longer to form, so don't use the color of the dead rock as an indicator that it's alive.