It really isn't deep enough to worry about at all. I would just pull off the loose piece and not stare at it too long. Rubber cement might stand out more than the missing rubber. I guess you could try Black RTV to hold it down, but ehhh...
The rubber cement isnt a bad idea as far as the look goes, but those mud grappers are probably at least a load range D if not E, so you'd need to take out a lot more then that to be worried!