I am not sure about the impact of enabling thin-enabled feature for virtual-volume on 5.5.  But here are the limitations of using thin enabled feature of Virtual-Volume: (Documented in page 36 in Release notes of 5.5)
Hi, Customer wants to use command “virtual-volume set-thin-enabled” on Geosynchrony 5.5 U2 with VPLEX Metro. All distributed devices are in production on customer environment, do you know if there is an impact on I/O or synchronization when issuing the command ?  This command is covered in the 5.5SP2 CLI Guide ([URL] p.557 and I looked in the 5.5SP2 Admin Guide ([URL] p.98 “Understanding Thin Provisioning”, but there is no footnote about an impact.  Thank you for your help.  Best regards,  Cécile
impact of command “virtual-volume set-thin-enabled” on DD