Something I noticed in the Fractal Continuum...

[Belhi]

My theory is that Garuda was an Allagan too. I also suspect the 'Lord of Serpents' or whatever it was from the Garuda mythos was a Chimeric construct.

As for the other beast tribes, I think some of them are the result of Allagan manipulation but not all. I think one of the FATEs in Azys Lla actually indicates that the chimeric creatures you are fighting seem to be a merge involving a lizard like beast tribe who lives in southern Othard, plus we know that Sephirot was worshipped by a plant like beast tribe. Considering they had the key, I think the Vanu Vanu are definitely candidates for Allagan created.

To be honest, Miqote are high on my suspect list for possible Allagan created races too. Its very likely that Allagans created Chimeric species for domestic purposes as well as war ones and creating a servant race would fit. It would also explain a lot of the cat like behaviour that Miqote culture seems to share.