Yes. You can install ORDS in 11gr1. Show how it works here.
you can use that tutorial for 11g too
Can you use ords with 11gR1 of the database?
It all comes down to the version of the JDBC driver being shipped with ORDS.
At some point, a newer driver will invoke a method not recognized by older versions of the database. 11gR1 is no longer supported (soon also to include 11gR2), and so the JDBC driver developers no longer test against those platforms. So while it MAY work, there is no expectation or promise by us to ensure it WILL work.