Some of the simulators, such as Real Flight, while not being perfectly the same as the real world, give you enough practice to readily be able to do the right things at the right times. A very large part of learning the basics to R/C flight is the ability to recognize what the plane is doing and the correct control response at the right time is to either maintain what you are doing or to correct what is going wrong.

In that sense, with enough practice, practice, practice, and practice, I believe that you CAN indeed learn to fly from a good simulator. Just don't get in a hurry to put the plane in the air for the first time. It would be better to go somewhere you can get a little help for the first few times up, especially to determine that everything is set up right. But it's not absolutely required.