Yes. Gaussia and Firefly luciferases catalyze the light reaction using different substrates. Therefore, the activity of each luciferase can easily be assayed from the same cells expressing both reporters. The GLuc and the Firefly luciferase activities do not cross-react with each another. The GLuc activity is typically assayed from the supernatant, but it also can be obtained from the cell lysate. The Firefly luciferase activity, on the other hand, can only be assayed from the cell lysate.