Chris,
RAID 10 is mirroring and striping. With thin provisioning, and pools, on the MSA mutiple RAID1 vdisks are striped (or wide striped) via the array controller virtually chunking up the volume instead of it being done purely at the RAID level. So, performance should be similar regardless of whether you have a RAID10 VDISK or multiple RAID1 VDISKS backing the same pool. I supposed you'd really have to run an exact test to tell but I don't think it's worth the effort.
Regarding your other question, you should be able to remove a vdisk so long as the pool as enough space to survive the removal of the vdisk. This will kick off a VDRAIN process and will take time.
and page 148 of
http://h20564.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-c04957376