Have seen valve stem holes welded and new holes drilled in Alcoa rims by a specialty welding shop several years ago. Not sure if it's still allowed but was at the time. Passenger vehicle rims are repaired all the time. Apparently skidder rims are repaired fairly often. If a rim is considered like a pressure vessel and potentially repaired as if it were a pressure vessel, then I think repairing may be an option. It certainly wouldn't be as simple as just welding the cracks up by anybody who can strike an arc. Preheating, ultrasonic inspection, hardness testing, X-raying and stress relieving may all be required so it would require a very strict procedure from an engineer and a highly qualified welder. Under these circumstances I can see why it wouldn't be recommended. Could a wheel be successfully repaired (depending how bad it was) I'd say yes but it would require a pretty extensive procedure by highly qualified tradesmen especially if reinforcement was being added. If nuclear reactor boiler tubes can be repaired, I'm sure with the right procedure a wheel could be repaired. Would it be worth the trouble and expense may be the bigger question.