Can you still be an organ donor if you have lupus?

Yes. A person with lupus, could donate any organ which is healthy enough to survive the transplant, and which that person could live without. Since lupus can affect many organs, this would have to be a very careful decision for the person, their doctor, and the transplant doctor. But it's possible.
Depends. Often times they will need to evaluate the specific organ(s) with imaging and biopsy prior to considering them for transplant due to inherent risks associated.