Yeah, Jefferson should be okay. 6'9, 230, 7 foot wingspan, savy defender, fifth year senior captain with some serious experience... It isn't like there are many college centers who are going to overwhelm him. As mentioned, he needs to defend, rebound, and score when it is a gimme. He and Thornton will have relatively limited roles, when you consider the scoring talent they'll have around them, and it is likely they'll do just fine, especially Jefferson.
When you consider Jeter is the backup, and he is 6'10, 240, with a 7'2 wingspan... That's good enough starting and backup talent.