I am not very familiar with the Multiplayer side of OFP, so do not take this as the last word.
I may be wrong, but you appear to be trying to make a system to catch potential cheats. From my limited experience I would say your idea would be almost impossible for two reasons:
1. The messages appear when the mission is initializing; that is after the lobby but before the briefing. I'm not sure detection scripts could be run at this time.
2. A problem with language, as the message is based on the stringtable.csv entry STR_MP_VALIDERROR, and so may appear in another language.
Sorry I could not be of more help.