Like an idiot I rushed thru this process again with ESX 3.5, swapping-out a DSS v5 DoM, thinking that the UUID issue would not arise (like it did with XEN). But I ended up having to use a v6 demo (the v5 would not run in 32-bit mode correctly), and I totally forgot about the IET->SCST issue. So had to go through the "resignaturing" process for storage definitions - it works, but less than ideal.

So a warning to everyone out there with XEN or ESX hosts - what may look like a simple change/update of DSS version, can bring lots of unexpected effects! Cheers.