Answer
Certainly. Nobuo Uematsu has indeed composed music as a freelancer for video games outside of Square Enix. His notable contributions include music for games like Final Fantasy Tactics Advance (2003) by Squaresoft (now Square Enix), Blue Dragon (2006) by Mistwalker, Lost Odyssey (2007) by Mistwalker, and The Last Story (2011) by Mistwalker.