I never thought of it but configuring an iPad for emergency use makes sense for a lot of reasons.
The point you make about storing pictures and videos for replacement reasons makes a lot of sense if all you have after a disaster is your iPad as you deal with emregencey officials and FEMA. You have your internet connection and your documents right there with you in a lite weight device that has an enormous battery life for a hand held tablet.
Plus as you shelter in a storm center and the power fails you are still good to go if wifi or the cell system is still operating. And if it is not, you can always read a book for hours or play a game while you wait. If the power comes on you can recharge your iPad in four hours or less for another full days use.
If you have a car you can recharge from that while idling.
You can pull up a large dynamic weather display to watch a hurricane land fall as you shelter down.
There seem to be so many pluses over a Kindle or even a relatively short lived iPhone.