In Final Fantasy Tactics A2: Grimoire of the Rift, I've recruited humes, bangaas, Nu Mous, Seeqs, and a Gria, but I've yet to get the chance to recruit a moogle or a viera. Is there a prerequisite condition to be able to recruit these two races?
For Moogles, there is no requisite other than being in the right places (Goug and Bisga Greenlands, if I recall correctly) at the right months (Goldsun and Silversun).
For Viera, you need to have completed the Moon Seal quest first (comes after the Star Seal quest). Then they'll have the same essence of being at the right places in the right months.
Just to be complete, Gria are the only race besides Viera who have a prerequisite. You must have access to Fluorgis first before they can be recruited, even though they also can be found in Zedlei Forest.