No it doesn't, I have it installed here and I don't have Rosetta. System requirements on the box says nothing about Rosetta and there's a big Universal binary icon on it as well.
If you didn't use Terminal to install Office, then you must have either upgraded Snow Leopard instead of doing a clean install, which would allow you to use Office without running the installer again, or you have Rosetta installed without realizing it.
Yes, I'm absolutely sure that I don't have Rosetta. It seems like an oversight on Microsofts part to require it for a universal binary, 3 years after PPC was continued.
If you didn't use Terminal to install Office, then you must have either upgraded Snow Leopard instead of doing a clean install, which would allow you to use Office without running the installer again, or you have Rosetta installed without realizing it.