Should cement be placed under concrete slabs for driveways or is sand enough?
You do not want to just place the concrete tiles on native ground soil. A proper installation would be to dig out the native soil down to a solid base. Then lay in a layer of crushed rock to aid in water drainage. Directly under the concrete tiles would be some sand that makes it possible to level and even out the tile installation.

With the correct materials that are properly packed in and if the water drainage from the area is implemented correctly an installation should stand up well without adding concrete under the tiles. But keep in mind that they will move around if there is winter frost action, an unstable base soil, very large vehicles driving over them or if there is a regular flow of water over and between the tiles down into the base materials. This movement can be mitigated by placing concrete under the tiles but there is a tendency to make this layer fairly thin and this can still crack and allow tile movements. 

My recommendation, if you want a driveway that will stand up to these stresses, would be to not use these tiles at all. Instead put down the crushed rock base and sand as a base. Then place in heavy duty wire mesh AND rebar in both directions in a manner that it ends up in the concrete as opposed to laying on the sand. Pour concrete to a good thickness (using 2x6 forms is far better than using 2x4 forms). Once the concrete is poured and being finished there are any number of techniques that can be used to make it look less like a slab. The simplest would be to surface groove it to look similar to the tiles. Other techniques include embedding brick borders, pebble surface finish, or even brick like patterning rolled into the surface. The latter is often done with the concrete dyed a reddish color.