The only reason I would see multiple versions of the same job as a possibility is if you could indeed customize/evolve your job's skills in a variety of ways as we discussed in another thread.
If that's true, then it's possible.. but wouldn't necessarily be so, as I don't think your skills are tied to a single weapon, but a weapon type. If all that were so, you could have more than one set of skills for the same class.. though it wouldn't be tied to a specific weapon, would it? Not unless your weapon is stays with you from beginning to end, and changes it's look based on skill level rather than substituting it out for a stronger version of the same weapon type. Hm, this is really a different topic entirely.
Potential evidence for the multi-weapon theory is in a screenshot I've posted a few times that show extremely similar looking mages, one holding what may be a different weapon type...
If that's a handheld weapon, it supports multiweapon theory. If it's a staff with the shaft obscured, I'd still be convinced in single weapon theory.
And, while I don't think this next example is in the same class, there's also that other mage, not wearing the Thaumaturge gown, that casts a protective bubble around herself/party members. This person seems to have a different weapon type from the apparent Thaumaturges.
It'll all become clear as new info rains upon us!