You would never use deadline in the same sentence with "is due by" since deadline is a due date. "The deadline for the conference's full-text paper submission is August 23rd." "The full-text paper submission for the conference is due by August 23rd."

It's almost correct. Since you've said 'submission deadline' at the beginning of the sentence, you don't have to say 'due by'. So your sentence should be "The full-text paper submission deadline for the conference is August 23."