Will you have scooters or such for people to rent that have handicaps when walking distance?
The ICC does have some wheelchairs for rental, but they are first come, first serve and are obviously ONLY for use in the convention center itself. Now, I am not sure if there are any differences in the rentals for an event the size of Gen Con, but I would not count on them being available. If you will be a mobility device, especially if you will need it anywhere but the ICC, then you will need to find another option.
Looking at the convention centers web site can confirm first come first serve, but found this site where you can rent a scooter in Indianapolis. scootaround.com
Hopefully that helps.
I was going to recommend scootaround.com. I rented from them several times over the years. I am not using a scooter this year, however. :)