In the Blue Angels FAQ it states that Fat Albert is made up of 7 crew, two of them being loadmasters. Why would you need loadmasters for a demonstration aircraft?
Fat Albert’s primary purpose is actually transporting spare parts, tools, and maintenance personnel from show to show. Performing demonstrations is more of a byproduct of being part of the team.
Most crew-served aircraft like the C-130 fly with a standard number of personnel in each crew position, but that can change depending on the mission. For example, a local area, post-maintenance check flight may fly with a minimum crew of two pilots, a flight engineer, and a first mechanic to assist with any items in the back-end such as opening hatches to ventilate smoke and fumes, manually cranking down landing gear in the event of a hydraulic failure, etc. (which loadmasters are also trained to do).
A normal crew for most missions contains at least one loadmaster, but depending on the amount of cargo and available personnel, it is fairly common to have two assigned. Lengthy training missions may be augmented with additional pilots and navigators.
For the logistical support missions Fat Albert is tasked with, there definitely needs to be a loadmaster in the crew. Fat Albert has two, not because it is necessary to have two on each flight, but because it is a small team on a tight schedule so there needs to be some redundancy in case one is injured or falls ill.
FYI, in addition to normal flight duties, on a demonstration flight that included a JATO shot, it is the loadmasters in the back who pull the jettison T-handles to dump the spent rocket bottles following the intercom command of the pilot.