Maybe you can’t hear it if you’re playing it, but It wouldn’t surprise me if other people can hear it just fine. I also tend to use louder whistles in larger sessions. But it’s a known phenomenon that whistle players underestimate their volume, which can lead to the problem of overly loud whistles.
I play the Highland pipes, and NO, you will NOT be heard , even with a single piper, UNLESS you are miked and have a good amp.
There’s you’re answer to your question. 
So we have mayo_piper saying it will not work. And we have Kenny Hadden, one of Scotland’s premier flute and whistle players saying it will work. Where does that leave us?
Recording, anyone?
With all due respect to Kenny - was the piper in the session playing Highland Bagpipes, or a quieter version like shuttle pipes or uilleann pipes ???
Kenny is not going to mistake one type of pipes for another. You do get highland pipes that are set up quieter, the shape and acoustics of a room can make a difference and it depends where you’re listening so sometimes maybe hearing a whistle would be possible, but I agree with Mayo piper - generally no chance.
Full set of Highland pipes.