Yes it is huricane season but huricanes are not like snow storms in Buffalo (where you can expect one or two a year at least). A huricane hits or brushes that area about once every 3 years. That means that the area is affected by huricanes for a day or two every 3 years. Those are pretty long odds that you’ll actually see a huricane in the week or two that you are there. Buy trip insurance if you are worried about it.

It is the time when the resorts are the least crouded. Ruins like Tulum and Chichen Itza are most frequented by tourists so if you go when there’s less of them around then the ruins should be less crouded. Although, no matter what time of year you go Tulum is generally crouded since It’s the most accessable from the tourist areas and cruise ships.

Alternately you could consider Ruins that are less well known or harder to get to. Coba & Ek Balam would be in th less well known category, they are easily with in a days drive of Cancun / Playa del Carmen. I have never seen more than a handful of people at eiter of these ruins anytime I’ve been there.