I've visited AKL many times and haven't noticed any major accessibility issues -- I sometimes have my wheel chair with me although I also walk.
Jambo House -- The walk way from the lobby down to the 1st floor where Mara (the quick serve restaurant) is located seems a bit steep and I couldn't figure out if there was an elevator that brought you up to the lobby. There was an elevator but it only seemed to bring you to guest rooms.
Besides the ground floor, the upper levels also offer viewing of the animals. There are outdoor viewing areas on these upper levels with rocking chairs and telescopes. You can also go outside from the DVC community hall room (which is located on an upper level.) Ask the front desk for a list of the animals and a map for where the savannas are located. The CMs outside the viewing areas can direct you also. Beware that you need to visit both Jambo House and Kidani Village to see all of the animals but it's only a 10 minute walk between the two if you don't want to take the bus.
allears.net has a pretty good description of what animals are found in each savanna
Depending on the time of day that you're planning on visiting, you might want to call the front desk and ask about the time that the animals are let out in the morning. I've visited AKL early in the day and the animals were not out for viewing because they were being checked over by the medical staff.
At night, you can go to a special viewing area and use night time vision goggles, which are kind of cool.
Have you thought about taking a semi private safari to see the animals? The program is called Wanyami Safari Resort Tour (this tour is only available to AKL resort guests.)