Heard back from Open-E support about using Xenserver in SCST mode and not having to switch to IET:

"Dear Sir,Our research team had tested the Cytrix Xenserver and we were able to make it work on SCST. The test was done on Open-E DSS V6 build 4362 and build 4221. You should be able to use SCST for XEN and Hyper V.If you have any more questions, please do not hesitate to contact me.Best RegardsShon (Sinan)Technical Support Engineer"Good news indeed!