The only circumstance I can see for interrogative is when you need absolutely no doubt that you are asking a question. "Interrogative, weapons free?" compared to "Weapons free?" over poor comms might prevent something s**t from happening.
In Arma though, not really necessary. Our communication transmission quality is exceptional at 99% of the time. The content may be garbage, but it gets through.

I've only heard of it in Gen. Kill and don't remember it ever appearing in the book written by the reporter or it's counterpart "One Bullet Away" by the platoon lieutenant.
There is a small amount of justification for it though, there's maritime signal pennant called "Questioning (INT)", as in INTerrogative and the term has probably just hung around since then despite having been phased out with the introduction of radios.