I just recently noticed similar construction on 650 manifolds. I presume it's purpose is tuning/balancing the two different manifolds. Delkevic systems have this as well.
I would leave the dent alone if it was my bike, as long as it hasn't rubbed through and leaking exhaust. It doesn't appear to be flattened to an extent where it would restrict exhaust flow enough to diminish power or cause overheating.The look of the damage doesn't bother me at all, but I was worried it might restrict gas flow. There are a few pics in my first post, try clicking the photo or using the arrow on the right side of the picture to scroll through.