It is very important that your father be able to complete the skill. It is a standard, so if one can not complete it, one should NOT be issued a certification. That said, the RSTC standards do allow for someone to use mask, fins and snorkel to complete the swim test (NOT the survival float test though), but it must be for a distance of 300 yards instead of 200 yards. Some find that way more comfortable and less fatiguing. I know some Instructors that will allow mask, fins and snorkel, and some that won't. I think many just don't know it's in the standards. As well, there is nothing in the standards that says the swim test must be completed before other in-water training, it's just the way it's usually done. Again, I know some Instructors that will allow skills to be completed out of the general order, and some that won't... often, the training agency dictates this.