We actually ran this as a joke a few months ago. Unfortunately the existance of Savannah Plateau M biomes meant that there are seeds where you just spawn at sky limit.

Animals in minecraft are placed depending on the order in which the chunks around them are loaded. In order to get sheep reliably you should experiment with different render distances and make sure you run on the same path (or close to) every time

Another reason is that the seedfinding project is far from over - and trading seeds are something on our radar this summer. Personally, I would advise everyone against subjecting themselves to the SSGP seed, since a major improvement over it should be coming once we are all done our final exams and currently the RNG is unbearable.