They are smaller than revival zones at least, though they are a good ballpark to use just to help split things up a little. LBML maps only show server-wide resources found within the last 90 days, so they're very coarse for any resolution.
In one server I mine, you can see the resource distribution change three times as you head south to north once you have logged enough on LBML. I can't say as much about east-west on that one yet, but there are definite areas within a server where resources are completely different. I
It's possible that maybe rarer resources have some sort of smaller zoning within, but I haven't seen anything yet that would differentiate that from just normal variation of rare resources or confounding between location and timing (i.e., mining when a certain resource is really common, but that "pocket" doesn't exist anymore because availability changed over time).
In another server, I can find Force Nexus all over, but the southern 1/4th of it doesn't have any without much change in the other resources. That could mean that it isn't a case of distinguished zones being set up and figuring out what's within a zone in that order, but that from a programming order perspective, each individual resource is given a zone where many overlap and can give the appearance of a zone with a specific loot table to pull from the mob end of things.
So tl;dr, you can find definite zones, but the time factor makes it tricky to really narrow it down. There's a lot you can ponder about, but once you mine an area enough to get a good average of MU over time, that's probably the simplest and best data to get.