1997 GMC C1500 Ball joint replacement

I don't see the cracks you're referring to. I DO see what looks like dimples in the middle. There's two possible reasons for those dimples, assuming they weren't there originally. The first is when pressing in that style of ball joint, the pressure must be placed on the outer circumference of the housing. On the other side of the control arm, there's a cone, much like a piece of pipe, about 2 1/2" in diameter for the housing to go into. A plate is placed over that cone to give something for the giant c-clamp to pull against. It is possible for the stud to get caught on that plate or the small hole in it, then the pressing action puts pressure on the stud. That pushes the ball down into the housing where it can push the center down, as shown in the photos. That entire plate is normally flat, but that circular line, (pretty red arrow), suggests this plate was designed this way to be curved to accommodate the joint's ball. If that curved part was caused by pressing the joint with the stud caught on something, it would not be that perfectly-shaped. Also, to cause that damage, the stud would also have been damaged. You'd see the evidence of that by the mashed first few threads on one side of the stud. The mechanic would have had to grind or file them to get the nut started.

The second thing that can happen is because of that curved plate, the pressing plate might contact the rounded center and dent it, (nifty blue arrow). The first concern is if there's supposed to be a grease fitting in there. If these were GM replacement ball joints, there will most likely not be grease fittings. The aftermarket suppliers, Moog in particular, do a real good job of developing problem-solver parts to address shortcomings of original parts, and will almost always have grease fittings. If you see a small threaded hole in those dents, where are the grease fittings?

That curved area could also be a pocket meant to store excess grease in which case the dents are harmless. Each ball will be under some pressure in its socket, either from a heavy spring or from a plastic ring. That pressure is high enough to prevent those dents from forming if those plates were able to make contact with the balls and impede their free movement. If you have not noticed hard steering or any unusual binding, there is likely nothing to worry about. Be sure to hang onto your paperwork though in case a problem does develop. If the pressing action caused something to deform inside the housing, looseness will likely develop very soon and you'll hear clunking noises over bumps. If you run into that, return to the same shop right away before any warranty runs out.