For example to send a numeric value from one to the other?
On the other hand RobotC is supporting Bluetooth upload/debugging. This means that it is accessible. My first instinct would be to look at how RobotC did it (if the code is available). My second instinct would be to find if somebody already hacked the EV3 brick using C code.
No, Robotc does not yet support Bluetooth for the EV3 - I even tried doing it with the labview software and it gave me an error message when I ran it on the EV3 brick