I think there is a lot of space between the walls and the racks. The rack ends will take some of the space. Here is an old pic I took.Tile backer board is not as hazardous as the Hardie board siding. Most of the hazard is in the cutting for the released silica.
If you put it on the interior what does that do to your racks?
There is a support piece across the side that is over 1/2" and the rack sticks out even further.
I will look up tile backer board.