If Hi-Tech modeled the 152.4 mm ML-20S gun-howitzer correctly ... there would be no question. The in-game Tiger II would have a genuine threat from the ground.
So I say if anything is going to be added to this "game" then the JSU-152 and/or the SU-100 should be top priority if there is going to be Allied vs Axis sides. If not then we'll all jump into Tigers and Panthers and keep having Big-Cat Fest 2013.
HE rounds bounce in Aces High. I suspect that either the ship guns are modeled differently, or there exists a KE/thickness threshold necessary to penetrate armor with an HE round, or both.
The latter is certainly true for tank guns currently in game, given that you can penetrate the weaker areas of a tank with a high velocity HE round, but not a low velocity round, such as from an M4(75), or Panzer IV F1.
Anyway, given the thickness of the Tiger IIs frontal armor, it's probable, bordering on certain, that the Tiger II will still be nearly invulnerable from the front, it the modeling remains consistent.
If they model it as a ship gun, then it will be heavily perked.