Pretty much all of the obvious things apply- for example, it should be obvious that you are only posting art which is yours.
If it seems like it would be against group etiquette, then that's a pretty good hint that you should not do it.
The admins aren't so active anymore and so it would be preferable that you contact the Founder directly by note if you have something pressing to say. He probably won't get to it until after a long while after you've posted it if you post it on the group page.
To be specific, an "unseen" equine artist is considered to be one that has less than 500 watchers, or otherwise doesn't get a whole lot of attention on their equine-specific pieces.
It is preferable that you do not try to submit something to our "Favorites," as we do not accept those. Just submit it into the gallery.
Any art with an equine or equine-like creature as the main focus is permitted. Any horse-like fantasy creature, for example, a pegasus, is allowed. And any horse-like animal, for example, a zebra, is also permitted. Do not submit pieces that don't contain any horses or horse-like animals, or aren't even related to horses.