I don't know if ballistic shots that have passed accuracy check and have score a "hit" can collide with unit that stand between gun and target or if collision hit checks are only for shot that have "missed".
I guess I can test with one of the high accuracy TDs at some point.
I tried this on the test range map with cheatcommands and a 100% accuracy shot will go through other vehicles and terrain*.
I basically put a JPIV to shoot a JT, while there were a bunch of other JTs in the middle.
In regards to terrain, you know how if you delete a base building the ground below sunk? Well i just parked a JP4 so it was basically below ground.
Not that I didn't trust your test, but how did you set it up? I am pretty sure that in the editor there is a value that allows a projectile to travel a certain distance without collision. At least in the case of the terrain it could be an explanation, and depending on the setup of the "vehicle block" test it could be as well.
My take on this was that I sometimes try to save a damaged vehicle by parking a healthy one in front of it and it works surprisingly well. Therefore I thought that all ballistic projectiles have collision checks.
Second, in the case of ATGs (most notoriously the Raketenwerfer) but also some other vehicles I see regular collisions with world objects as well as terrain (for example, in rails and metal a bunker or OKW HQ that is placed at the sloped hillside is near indestructable by ATGs because they will just fire into the hill). So that in turn would mean that either ATG projectiles are handled differently from tank ones or that fences etc are differently handled than all other objects (which seems to be the case as posted by Vipper).
Obviously I might have just been lucky plus there probably is subconscious confirmation bias, but overall I had the impression that ballistic objects can be somewhat reliably "intercepted" (more so than those ~20% chance of intercepting a scatter shot).