The primary concern is communicable diseases and other public health issues. Your father’s health concerns may not be a problem.
At the U.S. Consulate processing stage or if applying in the U.S. for the conditional permanent residency a medical report is required for each applicant. The medical report will indicate if there are any grounds of inadmissibility. The facts of your Fathers medical condition, on the surface, indicate that there are no grounds of inadmissibility. That is, he has no contagious diseases.