A very simple, easy answer..Pick out the 5er you want to purchase then, invest a phone call to the manufacturer of the 5er and ask them what THEY recommend. If the manufacturer tells you it doesn't matter to them if you use GN or 5er hitch, do what you want. BUT, if they recommend a 5er hitch to tow their 5er with over a GN, then I would follow the manufacturers recommendations to keep from causing any possilbe damages.
I alway's read where no one has ever seen these damages...I have, so that either makes me a liar, which I'm not, or proves that towing some 5er's with a GN hitch can cause some structural damage. What I saw was sidewall delamination. I've also seen welds broken around the pin box where welded to the frame and towed by a GN hitch...
5er's are built differently than horse trailers. Some 5er's can be towed with GN hitches, some aren't recommended to be towed with GN hitches. I would do what the manufacturer recommends, nothing more, nothing less.