Hi Peter,
Installing Service Pack 1 for SQL Server 2008 R2 should have no impact on your Project Server 2010 environment.
But it is strongly recommended to test it first in a test environment to make sure everything still works as expected after installing SP1. Especially if you have a non-standard environment (non-English language, different localization settings, custom reports,
...)
I hope this helps,
Hans
My EPM blog:
Projectopolis