It depends on a game and the definition of 3D. While many 3D games on Xbox 360 require HDMI for 3D support, there are some that can be played in 3D even without HDMI, if you have other proper means for the 3D viewing. There has been some debate about what does and what does not count as "real" 3D, but in its simpliest form, even red/green- glasses count as 3D. Also, there are some stereoscopic 3D video glasses (such as older Vuzix Wrap video eyewear glasses) that can be connected to Xbox by using composite connectors or similar input solution.
Some Xbox 360 games that can be played in 3D without HDMI (Side-By-Side, Top-And-Bottom, TrioViz or anaglyph) are:
- Assassin's Creed: Revelations
- Assassin's Creed III
- James Cameron's Avatar
- Batman: Arkham Asylum - Game Of The Year edition
- Batman: Arkham City
- The Dishwasher: Vampire Smile
- Enslaved: Odyssey to the West (Requires "Pigsy's perfect 10" DLC)
- Gears of War 3
- Invincible Tiger: The Legend of Han Tao
- Sega Vintage Collection: Alex Kidd & Co ("Super Hang-on" only)
There might be more, but these are the ones I have personally tested or otherwise know for 100% certainity. I typically use Vuzix Wrap 230 Video Eyewear for 3D gaming.
Of course, using HDMI for 3D means increased clarity and sharpness in graphics, and for some 3D games and formats it is an absolute requirement.