Although there is usually no park ranger in the area to check if you have a park pass (or a climbing permit for that matter, in case you go without a guide), that doesn't exempt you from buying one. It only means that you are very unlikely to get caught if you don't.
Apart from that, it's good to see another peak in the Cordillera Blanca on SP.
"After the first glass, you see things as you wish they were. After the second, you see things as they are not. Finally, you see things as they really are, which is the most horrible thing in the world."
--Oscar Wilde on Absinthe