From limited experience with race car wheels, the problem is surface cracking that can cause catastrophic failure under stress. I never heard anything about internal cracks. We used a fluorescent spray and a UV lamp for periodic inspection: spray, wipe, go somewhere really dark, inspect with UV light: the spray sticks in any cracks and they showed up very bright green. The cracked wheels (not many but not unknown) made nice coffee table bases with a disc of glass.
