I had issues a couple of months ago when using DSET 3.3 and ended up using the LiveCD option. Today I tried again with DSET 3.4 but got same results.
"Failed to gather Chassis/Storage data. Check the IP Address, credentials and namespace."
It turns out that options lg,sw,ad don't work well against ESXi - 5.1 in my case.
Selecting st,hw only, worked fine on the other hand. I think those are fine for Dell to start working in your case.