Is an executive chef the same as a head chef?

No. A head chef is usually the chef in charge of a single operation and is a "hands on" chef. An executive chef is a chef over multiple operations and works more in an office style capacity leading other head chefs or chef de cuisine. You will usually not find an executive chef on the line during the Saturday night rush...you better find the head chef on there though. Some operations will title a head chef as an "executive chef", but this is just dressing up the title.

One is the same as the other just different ways of saying it. Executive chef is a term used in hotels with large kitchens that have many different chefs employed. Different answer I have answered this on an alternate question. See http://wiki.ellenow.com/Q/What_is_a_master_chef