Israel keeps track of radio traffic in Syria from their Mount Hermon listening post. We do the same from space with the large NRO satellites.
Syrian officials certainly know these facts. So why would they have radio conversations about a chem attack while knowing the conversation will be picked up? Are they really that stupid....
What I think would be more important than the idea they were talking about chem attacks (which have been an issue for at least a year), would be 'what did they say'.
You will never be allowed to hear it, because it would make a farce of the whole claim that the 'regime' did it.
Besides, my sources tell me that the chem weapons were set off in underground tunnels that passed under various housing areas, so that the rebels could make sure they got a bunch of dead citizens to use as props.