We weren't checked at the gate. So I can't answer that. I don't think they'll tell you your not allowed in. Probably just tell you, you aren't allowed.. and tell you that if you're caught, you might get it confiscated. Big maybe. We had a pretty obvious bag, and we weren't checked..
My recommendation, maybe go early or where ever there is a big crowd... I doubt they'll take the time to search everyone if there is a big crowd.
I wouldnt worry about taking pictures with a DSLR in Desjardins. Anyway, if anything happens, you'll probably get one warning.. tell them "You didn't know" no matter how stupid that sounds - at that point, just put it away.
BTW - Not sure if you've ever been in Desjardins. But I can say I've been everywhere in the Bell Center [except the Lounge or pressbox].. from the wall at the top of the Bell Center to tapping on the glass behind the net... I had a few Desjardins seats one year, right in the middle of the ice, and besides AA seats. Those Desjardins seats were my favorite. You have a perfect view, you aren't too low or too high.. and the food is free, endlessly free... doesn't get better than that (even if some of the food isn't always great)