Is your Jeep lifted, and by how much? It is normal for caster to be reduced as lift is increased, and you can compensate for this some by shimming out the lower control arms at the frame mounts (I'm assuming you have stock, non-adjustable LCAs).
If a line drawn through your ball joints is straight up and down, then you would have zero caster. It would take a lot of lift to lose that much caster, and you would probably need adjustable control arms to correct it, and then you'd have to worry about pinion angles. It would also make the steering really twitchy and dangerous (aside from any death wobble, even). The steering wouldn't have any self-centering force.
If you're not lifted then I doubt you have zero caster. If you do, then something is wrong with your control arms or axle housing. When you look under the jeep at the knuckles you should see a noticeable backwards inclination of the line between the two ball joints (the top joint is further back than the lower).
My guess is that you're not measuring it right. I haven't tried to measure it myself but it looks like it would be difficult to measure with any precision, at least with any tools I have. I'd take it to a good alignment shop and get a printout so you know where you're at on toe, camber, and caster.
Besides, I don't think caster would actually cause death wobble. The self-centering force it gives would help dampen the wobbling, sure, but I don't see how it could start the thing wobbling in the first place. I think DW always comes down to slop somewhere in the suspension or steering. That enables it to wobble, and then something like an out-of-balance tire or a pothole or whatever gets it started, and then the oscillations hit a special frequency that amplifies the wobbling until its uncontrollable.
You didn't mention checking steering components. Have you checked your TREs, ball joints, unit bearings, and steering box for play?
(P.S...just so I'm clear: if you determine that you DO have zero caster, then by all means, you have to fix it. I'm just saying that I think it's unlikely if you're not lifted).
Good luck-
Robert