The pipe dent may cause general performance issues, but I wouldn't think it would cause tuning issues. Odds are, your a bit lean on the high speed needle.
You can get most of that dent out of the pipe with some creative plugs, water and a freezer. I've removed large dents from pipes before by plugging the stinger, fill it with water, plug the large hole the header connects to without spilling out any of the water, then put it in the freezer and...