I cure hides all the time and I have to say I have never heard of chewing to preserve. The Native Americans used to chew finished hides to make them soft. I personally use the animals brains and wood ash and it works very well....Ya there is brains and waste that work but chewing seems easy, also I'm sure you catch up on calories.
You will identify with this I bet.....Hide scraper that started as a tomahawk head till it broke during knapping...Chewing hides is not does to preserve, but to soften. I have never personally chewed a hide, except for some very poor employees. Back to the topic though, I have done some hide work. I made a very nice rifle scabbard (Hair on) out of a blacktail buck I killed one year. I brain tanned it. I currently have a few elk hides in the freezer which need some attention.
I have tanned most everything and yes all critters have enough brain to tan its hide....IMO and based on SERE "C" training...every animal has enough brains to be used to tan the leather it provides. Chewing the skin is a good way to get microbes and bacteria into your body. Nothing raw (especially warm blooded, Red meat animals) should be going into your mouth in a survival situation unless you think Hershey Squirts is a fun ride at Hershey Park.