If you have hoppers, or plan to do less "crowded" things after EMH / later in the day at AK, I'd be very confident in having a great day. Make sure the stuff you want to do is open during EMH. You'll probably get to walk on Everest several times. For my last AK am emh, we waited for FOP for 20 minutes, walked onto Navi, then bee lined to Everest for 2 front rows, then to Dinosaur. I don't think Dino was open during EMH, but we were able to walk on 2 or three times, no issue.
If you do go to Am EMH, remember to get there early to maximize your time. Most people TRY to get there on time, but life happens. I'd suggest making it a point to get there 30 minutes before emh starts to get situated. Most of the herd will head to Pandora. My guess is that Everest will be a ghost town for a while, since it's a bigger "more thrilling" ride that not everyone will do, so if the safari is open, that might be the best choice for your first attraction.
We are early risers, and we also use hoppers, so, we always go to am emh, then leave. An emh park will probably be more crowded because resort guests will plan to be at that park to take part of the "benefit" but if they do not have hoppers, they will need to stay in that park along with the other guests that cannot take part in the benefit. The guests that do arrive on time to take part in the benefit will have an opportunity to do some attractions with low wait times before the masses show up. The guests that plan to take part in the benefit, but don't get there in time...grrrr that happened to me once a few years back. The disney bus service got me good...grrrrrr.
My opinion is that am emh is great, however:
You have to get there early and ready
You shouldn't spend time waiting in lines that detract from your time that you could have spent more wisely.
So, basically, we always do am emh, then hop to a less crowded park, but we plan it out. If we did not have hoppers, then we'd still do am emh, then devise a plan to do our fastpasses and lesser tier attractions / shows when the park should be busy.