I run a york rake equipped with scarifiers to maintain a 1/2 mile long gravel driveway. To be honest, it does a great job without the use of the scarifiers. I think I have only tried them twice and the driveway is so compacted that they really didn't help. The tines of the rake are great at popping out small grapefruit sized rocks and leveling off the gravel. I usually angle the rake to pull in the edges first and then regrade the middle.
The rake that I have also has a rear blade that swings down in front of the rake teeth, but I also have not found a reason to use it on a gravel driveway.
Good Luck!