Hmmm, complicated question. Knights are considered nobility (though at the low end of the scale). But they are used to having contact with fighter types of lower status, so there's no reason they'd reject Admund out of hand (he's not some lowly street rat). He'd get a chance to speak.
Dieter isn't a knight - he became champion by winning the challenges one year. He's just a normal guy.
As for the Knight Eternal, if you speak to him you'll find out what his personality is like!