You never know what may happen, anywhere.
We've spent quite a few August nights at anchor and I don't recall anything too drastic for wakes. We dragged once when the wind piped up, and got a mooring(many say that's impossible without a reservation,...) It is not the best anchorage from any angle, but it's not the worst we've seen.
The moorings are pricey but for how often we go(from Maine), what the heck. We like it for provisioning(good market), the bus service to places too far to walk and the dinghy sailing is great.
September is a good time to go to the Cape from Maine(for us). It's sort of like stealing an extra August week or two and the crowds are gone right after labor day.
For instance, we were the only ones on the two Menemsha inner moorings last visit for one night(had company the next). Only boat anchored off Edgartown(not counting +100ers farther out) and the only boat anchored for days inside Cuttyhunk. In fact, there were very few on moorings.
We're headed there next week(weather permitting) and hope to get to Nantucket. Off season rates,...
My profile pic above was taken at the Head of the Harbor. Now that's an anchorage.