If the person brazing them is any good, they'll be fine. A good brazed joint is almost as strong as a weld.
The real issue is what the replacement carbide was made for? If it's for cutting metal, the binders aren't designed for the shock loading a grinder sees and you'll fracture the matrix. Carbide isn't a solid material like steel. It's a sintered composite of little crystals of carbide and a bonding alloy which holds it all together. Unless they're getting the tougher carbide designed for stump grinders, the replacements will never be as good as new teeth.