As far as I know it's not possible to enroll anything other than 2008 R2 into UCP. I found the following on the MS website.

"Before you create a UCP, review the following requirements and recommendations.

In this release, the UCP and all managed instances of SQL Server must satisfy the following requirements:

SQL Server must be version 10.50 or higher."

Let me know if you find out different.

Thanks.