Just want to add that I've used both FC Attached Tape and SAS attached tape in virtual machines based on vmware 5.5 and 6.0 without any issues.
The trick is to attach the entire HBA Card to the virtual machine (thereby limiting the VM from vMotion etc) - But performance and stability is super. Filling up 2 LTO7 tapes at max speed (600 MB/s) is possible.
Its not optimal, but if you NEED the tape server to be virtual, its a working solution. The solutions I've been involved in, have been to provide easy faalback to the old backup solution to restore old files from tape, by moving the HBA to the old backup server (that was virtualized and put on the same host)