Hi,
AFAIK the esxi5 doesn't support it any more.
Check here:
http://www.vmware.com/support/vsphere5/doc/vsphere-esx-vcenter-server-50-release-notes.html
(search for "tape")
I have here esx4 with lsi scsi /lto3 configured with passthrough - works w/o problems.
Reg
Christian