jartzh,
Here's a link to the US Forest Products Lab. book "Wood Handbook".
I believe it will answer most of your questions regarding finishing your bar top.
Scroll down to "Chapter 15 - Finishes for Wood". There is a lot of info on different wood finishes and their applications.
Table 15-3 shows different types of finishes and their effectiveness as moisture barriers. A Very Useful Chart !
Also, page 15-32 discusses finishes for items used for food. Maybe your bar top will fall under this topic.
Forest Products Laboratory -- Forest Service -- USDA
Hope the above link helps.
IMO I don't think that any type of finish will be 100% for you. On a piece of wood that wide (esp, Hickory/Pecan) you'll probably need to refinish on a regular basis.