Hmmm....looks like it is aok for grazing (at least to livestock )....I personally have no knowledge as to if a tortoise will want to eat it or not though?
Now, I have found conflicting info on the "oat grass"...there is a multitude of species and so I do not know????
Perhaps someone here will have better info for you....well, at least my post will give you a bump back up to the front....lol...