IMO Dragon Magazine is more official than other licensed material because:
1. Paizo was actually just the WotC magazine division at the time.
2. The majority of issues were actually published by WotC or TSR; Paizo only controlled it for a few years, and not even for all of 3e.
3. It's referenced as canon in 1st party books such as Elder Evils and Spell Compendium.
4. Most 3rd party licensed books only licensed their respective setting, but still used the d20 OGL for the rules. Dragon and Dungeon had full access to the IP, including the rules system and all official campaign worlds.
5. Paizo was contracted to produce the magazine each month, where other 3rd party publishers were basically "You have the license for X years, go nuts."