if it where up to me, I wouldn't mind if you did, however due to the terms and conditions of the default resources across all the RPG maker engines, there's some rules against it due to a lot of animals being built/edited originally from RPG maker MV's sprites. Now if you happen to own RPG maker MV and are simply using VX/VXA, you can use them since you own both engines and have fair use to the resources from both engines and can mix/match them.
Since the animals I've made are edits of MV, and it's simply a headache to keep track of what can/can't be used, I simply blanket it across the board as using them as if they where part of the defaults.
HOWEVER, since I get this question a lot, there ARE a list of animals within the set that are not MV edits and are 100% all on me, and I hate leaving folks out like that, so here's that list:
Pomeranians
Baby chicks
Seagull
Ostrich
penguins
Monkeys
All animals under the "very small animals" tag
All animals under the "fishes" tag
Golems
Walking mushroom
Mini mushroom men
Running radish
Kasa-obake
Kappa
Ghosts
Ariman
Catbear
Werewolf/wolfbeast
Behemoth
all animals under the "dragons" tab EXCEPT for the "dragon recolors" and "cute fat lil' dragons" (as the wings come from MV sprites)
I will allow any of these to use used across any engine, both RPG maker and non.
for any other VX/VXA animal sheets, I would recommend checking out grandma deb's post:
RPGMaker Web VX/Ace Resources Thanks to some initial hard work by Emmych, there is a Resource Showcase Directory for resources hosted on this site. It is currently under construction, so the "look" may be a little rough around the edges sometimes =] The directory is divided up into subheadings...
forums.rpgmakerweb.com