Since you asked what is allowed, rather than what we wear, the answer is "yes", you are allowed to wear jeans & shorts. We've seen lots of people who appear to have just come from the parks - sweaty, stinky, crabby kids, shorts, flipflops, tshirts, jeans, shorts, etc., etc. Not even looked at funny by the staff - no problem for them getting seated.
We go to there often & we get the Porterhouse. Only once wasn't quite satisfied with the steak, but it wasn't bad. One time, the Porterhouse was the best steak we'd had anywhere. So like all Disney restaurants, consistency is lacking. I ordered the NY strip once & it was not as good as the Porterhouse.
FYI - I judge on tenderness, seasoning/taste, quality (no grizzle, etc).