I've welded cranks. But, not for crack repair, only to re-build the journal after a spun bearing. It's not hard to weld a journal up and then turn it down to the proper size. Works perfectly on forged crankshafts. No problems with strength issues either.
However, cracks are another matter. As cracks develop in stressed steel, the structure of the steel changes ahead of the crack. In other words, it's weakened. A proper repair is often impossible in forged steel, without reinforcements. That is why one cannot simply weld automotive suspension components that are prone to cracking and expect more than a month's lifespan from the repair.