You mean somehow merging the tone and continuity of The Batman with the planned DCU? For several reasons, that strikes me as unlikely.
Generally, I’m nitpicky when it comes to “tonal” consistency within a shared universe situation. Now, we don’t have a lot of info about Gunn’s approach to Legacy. But we do know about the source material for the Woman of Tomorrow movie. And it’s fairly fantastical (as oppose to “grounded”). Therefore, by association, we might guess that Legacy will exist in this same fantastical sub-genre. Which means… there’d be a large “conceptual distance” between the world created by Reeves and the one that Gunn is in the process of building.