Not by themselves, but they can be a resource and workout tool to use every once in awhile. However, I would not advise someone to solely rely on them to greatly increase your vertical. If a player wants to learn how to dunk a basketball, the best way is to practice dunking on a lower goal. It practices your footwork and your explosion for jumping higher. To supplement dunking on a lower goal to increase your vertical, I would also recommend these exercises: (keep in mind when doing these exercises, you want to do them all with quick explosive movements that will replicate and reinforce the explosive power it takes to explode high off the ground)
-seated and standing calf raises
-Squats with light weight and fast explosive movements
-Lower back raises
All of these muscle groups help aid in the jumping motion, but as I stated earlier the best way to get all these muscle groups to work in unison is dunk on lowered goals. Plyometric type training may also present medical concerns for younger athletes that you can discuss with you doctor or trainer.