I think that this is a false distinction. As much as Durkula resents Roy, his biggest motivation is revenge on the Dwarven people. Because that's what Durkon wanted in his darkest moment. This can't be a competing priority against his loyalty to Hel, because completing Hel's plan is the greatest revenge against the Dwarven people conceivable.

I think that his own goals may indeed be more important to Durkula than bare LE-cleric loyalty to his deity. But those goals are practically identical, so it hardly matters.