Supplementing Farmer's Walks with your hexbar will build a stronger core, which could assist a little.
Like they said though, the hexbar definitely takes the back out of the equation more.
I have a hard time believing there is no carryover though. You train grip, leg drive, hip drive, you become accustomed to holding heavy weights, and most who say it doesn't carryover still claims it makes you stronger... So how are these gains not applicable? I'm at a loss a bit.