Yes, Shamans can equip a shield when using a 1hb weapon. They can also use a 2h blunt weapon but will not be able to equip a shield while using the 2h weapon.
The advantage with the 1hand weapon and a shield is that having a shield in the secondary slot increases the softcap AC value on the character. This "soft cap AC " is much more effective than normal AC values from other slots/buffs etc on any class.
1h blunt and 2h blunt are separate skills and thus have no bearing on one another.
EDIT : Most staffs are 2hand blunt weapons,though I've seen a few 1h blunt weapons with the word "staff" in their name.
Good luck and enjoy.
Edited, Dec 20th 2011 1:28pm by hexeez