Yes, because the welders qualified using an F-6 filler metal with the GTAW process. The filler metal for the dissimilar metal weld needs to be selected.
My recommendation is to use the following;
if the service temperature of the joint is BELOW 700 deg F, use ER 309 filler metal.
if the service temperature of the joint is at or above this temperature use Inconel filler metal. This will require you to qualify the welders separately for this filler metal (F-43), and a new welding procedure using F-43 filler metal.