So, getting back to worse centers than Semih Erden, there are two centers who are worse than Erden in all four categories of Offensive Rating, Defensive Rating, total rebound % and PER: Theo Ratliff and Hasheem Thabeet.
For centers worse than Erden in rebound % and PER, add Joel Anthony, Jason Collins, Hamady Ndiaye, and Hassan Whiteside.