I think gatekeeping a distinction between the DCEU and the Snyderverse, which overlap considerably, is just kind of fruitless. At the very least, ZSJL is highly DCEU adjacent, and I know you know that.
Even then though, James Wan has said that he tried to make sure that Aquaman was consistent with Zack Snyder's version of JL, and even talked to him about it at length to avoid continuity errors with a movie that at the time, was probably never going to be released. So I think that's a pretty good argument toward including ZSJL as part of the DCEU, even though it is an alternate version of another movie.