As of latest UCSD 6.5, it is a limitation on the out of the box Task where it didn't have an option to enable Thin provisioning on a newly created LUN.
However, you can workaround it through an SSH task. I have attached a sample workflow which connects to NetApp controller and enables Thin Provisioning on a newly created LUN.
Tasks Used:
Create Cluster Flexible Volume
Create Cluster LUN
Get SVM Name (Custom Task)
SSH Command (to enable Thin Provisioning)
The attached workflow was created on UCSD 6.0.1.2 (FYI)
Thanks,
Phani