The combination of tech possessed by NRO/NSA could make it easy to send false radio data from anywhere.
Here is what I would do if I had the resources...
It would be no problem to drop a tiny software-defined-radio somewhere in Damascus and have a language expert in Langley send down any conversation they wanted the Israeli monitors on Mt Hermon to hear. (The Israelis must be monitoring from Mt Hermon as it’s the logical choice)
The signal would go out locally on normal frequencies used by Syrian officials. The SDR could be planted in Damascus by a method as simple as placing it inside some common object and simply mailing it to someone. This is a technique also useful for monitoring radio traffic in an area that cannot be picked up by an NRO sat directly because the frequency is too noisy from other sources. The SDR picks up the traffic and relays to the sat.
It reads like a cheap spy novel I know but this stuff is actually possible.
Yes that would do it if the monitoring is just for the content of the message. However, these messages would be stored and when you check them in detail you can see the frequencies of the transmitted talk and if there are any distortions that can be compared to the other known radio transmitters etc. You can be fooled in the beginning but not after a couple of analysis. The take home message is no to trust the first analysis.