My calendar syncs with outlook, and invites seem to work OK. I can accept on either the phone or PC and it syncs. I have had some conflicts, which I think occur when I accept on my PC as soon as the invite comes in, i.e., before the invite syncs to the phone.
I do have my gmail calendar turned off in Accounts and Sync.
When you receive a meeting invite that comes from outlook does it go to your calendar on your phone? Mine does not. I receive the meeting invite as an email that has data in it such as "BEGIN:VCALENDAR"
I am able to sync the entry from my PC but not accept or decline via my phone. Also if I send a meeting request from my phone the recipient see's a meeting invite from my gmail account not my domain account.