We use weighted baseballs all the time in our facility. Both Oates' as well as the ones we specially manufacture.
You can see our guys pitch in the Pacific Northwest for yourself if you want to see the velocity. Don't need to take my word for it. Chris Carns (2014 Decatur, RIPS) threw 93 / sat 91 at a tournament in WSU, Julian Archuleta (2014 Peninsula, Krushers) hit 94 in a game, Herbie Good (2015, Auburn MV, Born2Play) hit 88 / sits 86. All of them started at far lower velocities than that.
It's not a quick fix, though. They use them on a regular basis even throughout the season. And we verified the safety and effectiveness of our program in our four camera high-speed lab and will soon be doing a large research study on them using wireless EMG sensors.
Should also be noted that they all throw long toss, lift weights, throw bullpens, etc. The best of my guys are training six days per week, even during the season.