I am planning to refill my large bike wheel bearing grease with Bellhammer metal grease. Once replaced once, it will not be replaced for 20,000 to 30,000 km, but will it last?

There is no problem using Bell Hammer metal grease for wheel bearings on large bikes.
Even though the metal grease feels like it is packed deep, in reality it is difficult to get deep into the wheel bearings, so the more grease you pack in, the better the condition will be.