I'm a big fan of both of them, and I never really noticed a similarity. Certainly, they operate within the same limited range (which is not meant as a knock on them) but I would say that, besides the obvious difference - the accents - Ray's voice is much more silky smooth, where Jeff's is more gruff. Both use their instrument to great effect.
Now go talk to your wife.
Cheers.
Now go talk to your wife.
Cheers.