Yes, but it's not a permanent default which is what is needed for perfect two way sync with Google desktop which all of us expected and desperately need.
I've used various custom ROMs and none make gmail the default calendar account. I too have looked into this but have to yet find a solution that makes gmail the default calendar acct. Pls post a solution if you find one!
Unfortunately, android calendars leave a lot to be desired, as far as I have found. I wish someone would copy the WebOS calendar (or better yet, the original Palm calendar, but with the integration of different calendars like WebOS).