Weapons don't work on shm pet.
You can buff them the same way you can buff players. Just their HP bar don't move when say you hit them with STA the way it does with players. (str,AC,HP,Haste, etc)
Haste and STR are probably the two biggest buffs you can give them.
I don't know the max hit of the max level pet, sorry.
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Wiki says max hit is 45-52. I can't confirm if this is true though.
http://wiki.project1999.com/Pet_Guide#Shaman_Pets