Director Krennic and Death Trooper viable without zetas?

I think you are better with just DT. Their synergy is nice but is it game changing? No.

A zDT is better than non zeta obviously but it's not going to make you jump much higher in arena and won't make you score crazy numbers in raids. There are many zetas that have in the past, or are currently, making a big difference in those categories so if you don't have it ready to go or to spare, best save for the next shiny thing that comes out.