I'm going to move this to the regular disABILITIES Board that deals with WDW trips. (you posted on the disABILITIES Community Board, which is more for general advice)
Here's an answer and I think you will get more by moving the question.
For the first (or only) show, people often start waiting in line 2 hours or more before the show, so it looks pretty daunting to wait for the show.
But, for the first show, they open the gates and start letting people into the amphitheater area about 1 1/2 hours before the show. Once they do that, the line of people who were waiting disappears pretty quickly as they walk into the show. People coming once the initial 'crowd' has entered will usually not wait in a line at all. They will walk in a continually moving line with gaps. The queue is VERY wide, probably 15-20 feet wide, so there is opportunity to walk in a quieter area with no one really close by. When you get just by the stroller parking area (about halfway in) there is a CM directing traffic. At that point, a CM would usually separate those with wheelchairs,
ECVs and GACs. Those groups get a CM 'escort' to be shown where to sit (other guests are just sent straight in to where ever the CM directing people to the area currently being seated go).
What happens if someone uses a GAC, without a wheelchair probably depends on a few things, like what they need and how busy it is. My youngest DD uses a wheelchair, but we have seen people with GACs who don't have wheelchairs follow the same 'procedure' as we have followed.
There are limited numbers of spaces for wheelchairs, all in the back row of the amphitheater, across the whole back row.
The 2-3 rows right in front of the back row are reserved for the rest of the people in the wheelchair parties and for people with disabilities/conditions that limit their ability to go down stairs to the further down rows.
Examples could be someone with crutches, cane, walker, etc who is not using a wheelchair. It may also be the family of someone with an invisible disability who wants to be at the back because they are not sure how the person will react. On our last trip, we had a family with a little boy who appeared to be autistic and another family with a child with Down syndrome.
Those people would have been directed to the area by showing a CM a Guest Assistance Card.
It is possible that the CMs might route someone with a GAC thru the dinner package entrance if they get there later because that would be the least congested/busy entrance.
For the second show, there are not usually as many people, but they 'hold' the guests for the second show until those from the first show have left. So, it may be more of a crowd waiting until the waiting guests have gone in.
Whichever way you go in, it is a long walk.