In my experience, evening EMH can be really useful for a lot of parks, Magic Kingdom in particular, due to the high number of rides that stay open to disperse already smaller crowds. And the later it gets, the more people go home. I remember being in MK at 3AM and walking on literally everything.
However, for Animal Kingdom evening EMH, it's harder to say as they're still fairly new (I've never been). Also, I think it's fair to assume that Pandora is going to be a mob scene at least for the earlier part of the evening. Maybe by midnight it will thin out, but even then it's hard to say for sure. Maybe someone else here will be able to help you better for Animal Kingdom specifically.
Overall, EMH is always one of my favorite parts of the day IF the crowd thins out enough and you're willing to commit to being in the park until the have to throw you out haha.