Spouses and dependent children are medically exempt - in other words, unless your husband has an illness that make him a threat to Canadian public health or safety, he cannot be refused PR status in Canada for medical reasons. See Sections 5.19 - 5.20 of the
OP2 Family Class Processing Manual He does not need to be afraid to disclose his condition, and any medications, etc., to the DMP performing the exam. The exam itself is basically cursory - height, weight, vision test, listening to the heart and lungs, etc., and then a chest xray and blood work.