Yes it is allowed. We are prostrating to Allah putting our forehead on the ground or Turbah. We are Not prostrating to the ground or to the Turbah. Those who prostrate on the carpet, are they worshipping the carpet?? Obviously no. Same with prostrating on the Turbah or Mohr or etc.
Names graved on the Turbah does not mean that we are prostrating to the Imams. We prostrate to Allah only.