I agree. It's certainly something good to include on the AACOMAS application under "Extracurricular, Volunteer, Community Service", but I wouldn't count it as volunteering hours on the MSU secondary. Sure, you
can... but they'll see it either way... and I think it may look like you're fishing for hours and potentially diminish other volunteering activities by association. Unless you can mention specific things you did
with student government that is of more benefit to others (e.g., cleaned up campus, managed bake sale for cancer research, etc.), I'd keep it solely on the AACOMAS application.
Just my $0.02.