No difference between hit sprites in a tank lusche, but if any of you have killed a panzer or T-34 with an osti, you will probably have noticed that the shell hits look identicle (yellow-orange flash followed by a little swirl of smoke).
Since the Il-2/Hurri IID do use AP rounds, they should have the same hit sprite as is used with tanks.
And lusche, I believe the reason they don't use the 30/37mm HE round hit sprite with tanks because it would look strange (not saying thats what it is, but thats just my bet). But the M8's HE rounds should look like that as well.
If you want to see what I'm talking about, go into offline mode, up an osti, and fire at the left side driver's compartment of the T-34, or just start hammering away at either of the tank's tracks.