Yes on the testing with the dark cloak morph and use of it successfully for several hours last night. It reduces fire siege damage via removal of the DOTs. Edit: my reply is confirming yes on good mitigation, but not of any particular %.
No I've not tested the shadowy disguise morph but plan to do so.
Today I need to finish testing of healing ward. Yesterday it provided no benefit. But the 6 sec duration made it clunky having the player fire at me in time to be 100% confident and we ran out of time.
At the moment, cloak, mistform and purge appear to be the only mitigation options for NBs.
Yeah yeah, red circles my ass... easier said than done when you've 4 of them converging on you from every direction and hitting for 20-35K. And siege shields don't move with you.