Nishko,
Mic input sockets want mic-level signals (typically microvolts or a millivolt at max.) The intercom probably has levels a thousand times too high for the mic input. All you will hear is massive distortion! You may even blow up the camera's mic input circuitry.
Ghenghis's suggestion about a lapel-mic slipped inside the headset earpiece is a good one and will work infinitely better than just stuffing an output of the intercom directly into the mic input on the camera.
Alternatively, find someone who will make a "pad" to reduce the levels to mic level. A couple of resistors will do it, but the values of the resistors will need to be carefully calculated to get the impedance and level translation just right.
The lapel-mic inside the headset is the best and easiest way to go, and you will have a very nice audio track.
"audio - ten percent of the shoot, ninety percent of the problems in the edit!"