I think it plays a larger role than you may initially think. I know of some current and former players that have had to take 17, 18, 19 credits a semester. Hockey is much more challenging to create a class schedule around that other sports. Sports like Volleyball, softball/baseball, and soccer only compete during one semester which allows many of the athletes to take a far easier course load during their competition semester than they would in the other semester. Coordinating your travel schedule with tests, essays, etc in a class can be ridiculously stressful. Although, I will say that many professors are very understanding about taking a test earlier than scheduled and are usually pretty good at making arrangements if the athlete is respectful and handles that business in a mature and professional way. A fifth semester would allow athletes to ease up their course load and spread it throughout an entire year rather than 8 months.
I don't know much about the money aspect in terms of scholarships but would a fifth semester allow a university more flexibility in scholarships? As in, making it easier for them to spread out their scholarship money to a whole year rather than larger sums of money only twice a year?
Another factor to consider is overall graduation rates of your team/program. A fifth semester scholarship would allow athletes who aren't being supported by their parents or an outside money source to take those extra summer classes without worrying about the finances. More semesters to finish all of the credits would mean that an athlete could finish in four years instead of five and thus increasing the graduation rates.