Hi Kevin, it is okay to use rigid lines if they are mounted on the same structure and some on this list do use rigid lines from engine to re-drive.  The key is to not have any movement from one to the next; from engine to firewall for example is not a good choice. I personally don’t use any rigid lines as though there may be no relative movement, I’m more confident that the flexible lines are better when exposed to vibration. You may want to use a mid-point adel clamp for security. If they are made from metal I would not fire sleeve them. There is a fire sleeve over my return oil line from re-drive to engine as it passes near my exhaust.

Jeff