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:
All animals under the "very small animals" tag
All animals under the "fishes" tag
Mini mushroom men
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...