The damage bonuses vs Fiend granted by Seraphic Helm and Seraphic Mail do not appear to be working.
I compared my damage values with a friend and we had identical numbers. I was using Seraphic Helm, Seraphic Mail, Omega Shell, and Leviathan Blade. My friend had Vog Cub Cap, Vog Cub Coat, Swiftstrike Buckler, and Leviathan Blade. All of our equipment was at max heat and neither of us had any UVs that affect damage in any of our gear. Our damage was equal for all enemies, including Fiends.