__________________ Level_ Pet Level__ Pet ~HP____ Max Hit
Companion Spirit______ 34____?-26_____ 850_________30
Vigilant Spirit_________ 39____?-28 _____900_________35
Guardian Spirit________44____ ?-32_____ 1200________43
Frenzied Spirit________ 49____?-36_____ 1800________51
You'll notice that you gain 5 levels and your pet falls behind. This is why they turn light blue or green.
Weapons do not affect shaman pets for dmg/dly ever, and no procs until IIRC PoP with the mage summoned pet only stuff. I could be wrong about that, but I've never tried or heard of a shaman pet with gnoll lariats.
They cannot Dual Wield ever.
Source:
http://www.pro1999.com/shaman-pets.html