I used a VERY thin layer of sealer. You will find answers on both sides here. Some say no, others yes, the main reason for not using it is for the NEXT time you have to replace the pump, makes the gasket harder to replace.
I like to use it because it helps me better visualize the bolt tightning, (slight ooze ) and it holds the gasket in place on the water pump when applied to the block
Good Luck