When the Revolutionary Army arrived to Tequilla Wolf, they were surprised to see Robin there, nonetheless, they revealed that they had been looking for Robin for quite some years, but were never successful.
Like someone said before, the Phoneglyphs tell the story of a civilization whose enemies are now know as the World Government. The Revolutionary Army, lead by Dragon, wants to fight that same Government. I don't think that they are simply a group of headless punks that were sad that the government didn't allow them to grafitti the walls. The Revolutionaries know how the Islands that do not belong to the WG feel, and they know of all the corruption that exists. Even though no one (almost no one) knows what happened in the Void Century, everyone with a little bit of intelligence knows that it is something the WG wants to cover up.
As of now, Robin is the only one who can read the Phoneglymphs, and the only thus the only remaining link to the Void Century. I believe that when Dragon started to look for Robin, he found something of great importance about it. Something that still wasn't revealed, but I'm sure it will be in due time. Likewise, the Revolutionary Army has extremely strong military power and espionage power. Both fit Robin's style very well.
Also sending her there to see the dark side of the WG even further, where it makes people that are not allied with them into slaves. Maybe as a way to keep her inspired
That would be why Kuma sent her there. It was not random at all.
Also I'd like to add:
Luffy - He was sent to the Island of Women, not to Rayleigh. He was sent there because they are the masters of Haki. Luffy was shown to possess a powerful dormant Haki, and sending him to a place where it would be sure he would experience it in first hand is quite an obvious choice.
Zoro - Yeah, you are right.
Nami - Correct
Usopp - The Boing Archipelago represent a great challenge for Usopp. He needed to man up, gain courage.
Sanji - Not because of Shemales. It was because of the Martial Arts and the Enhanced Food.
Chopper - Sort of, ok. It was because Torino Kingdom holds, probably, the most advanced medical and herb knowledge in the world.
Robin - Said above.
Franky -

, it was because it was the home town of Dr. Vegapunk, of course, the greatest mind alive in the world, one could say the best Inventor there is.
Brook - Yeah, I don't know either. They were having a satanical ritual, yet I don't know how could Kuma know this. The location where he was sent to was pretty random, unless I am missing something. Though one could say that Kuma knew that in that location, the Long armed tribe and the normal armed tribe were fighting each other. We know that they were doing it because they found the other to be really weird. Who is even weirder? Brook lol. I could say that they were known slave traders, that's why Kuma knew about them.