Terry,
I am sure there is/are one-off bikes that have been made to use diesel, but this practice is not used generally. Motorcycles are generally used for the exact opposite thing that makes a diesel so appealing for tractors. Diesels excel at work that is heavy and at low RPM; they are fuel efficient, particularly under a heavy load; and are very heavily made. These facts would not be as useful in a motorcycle, as they are lighter, and geared more toward recreational use and generally are not used day in and day out, for extended periods. That said, diesels are changing. About 15 years ago, I drove a new 6.5L diesel GMC pickup home from a dealership for a friend of mine who owns a dairy farm. It would barely get out of it's own way and got about 15 mpg. My diesel pickup 2002 model, will outrun my wife's dedicated sports car, gets 22 mpg on the highway, and will pull 12000 pounds (rated) easily. It will also last 300,000+ miles, will proper maintenence. So diesels are coming, and will likely begin to be real options in cars and who knows maybe motorcycles, too.
John M