Well, I know it’s the Akuma board here and it might sound a bit biased, but the match is in Adon’s favor, though it’s sure far from hard or impossible. All comes down to the fact that Adon wakes up so fast that we basically can’t do sh*t on his wakeup, and Akuma in this iteration is all about vortex. His high damage, and tricky ground/air game sure doesn’t help. That’s why we will all rejoice in AE, this matchup will be even, if not slightly in Akuma’s favor.
As far as your concerns with st.HK: that move is one of the best tools Akuma has, against those characters where the 2nd hit doesn’t whiff. As you know, Adon is among them, so we try to exploit that. The move leaves you at +0, so you can forget about punishing it. Knowing that though, you can adjust your game.
Since it doesn’t leave him at disadvantage, Akuma often tries to follow a blocked st.HK for more pressure. If you got 2 bar and you see your opponent go crazy after st.HK, don’t hesitate to DP him.
As far as normals go, if Akuma is on point and follows up with crouching Jab (3f startup), your option is pretty much blocking and crouch teching, or you can try your luck with your crouching Jab, but you’ve got to have the timing down (and it should just trade, so it’s not that much of an option imo). Also, be careful for counterhit fishing, if your opponent has conditioned you to stay put, he might wait a bit and then throw a quick normal.
Keep in mind that if the Akuma notices you mashing normals after the blocked st.HK, he might also go for a Fierce DP (6f invincibility) which will beat pretty much everything. Pay attention to his EX meter, Akuma doesn’t want to DP unsafely.
Backdashing is an option too, but a cr.LP OS Sweep/Raging Demon should take care of that.
Hope it helps, but wait for more experienced players to come, we’ve got several around here.