I think they are saying that AKC doesn't recognize the long haired dog as it isn't part of the AKC standard. Not that you can't have a long haired dog registered. It's considered a fault.
I suspect the temperment difference would be equal to the lines that more readily present long coated dogs.
Hondo Von Dopplet L Bauernhof "Hondo"- GSD
Lilie's Tug McGraw "Tug" - Golden Retriever
Maggie - Mini Dachshund (Rescue)
Lonestar - Texas Blue Lacy
Funyon, Ashe, Soot - Barn Cats
Scooter /1/2 Arabian, Shadow, Katie / APHA