Yes.

When I applied visa two year ago, I stated that Tibet is one of the destinations. My application was refused.  But visa officer called me saying if I decided to take Tibet off from the list, it would be OK.  I did.  Once in China, the visitors holding non-Chinese passports need special permission from Tibet government to go there.  Just as mentioned by others, they will group the visitors into tour groups according to country.  The fee is very high too, close to 1W for a week.