Yes, if you remove building/tree .pbo files, they not exist for you and you can shoot throuht it and move throught it.

You can also remove your gun sounds and other sounds your character/items make.

heart attack, it's a feature

Not a hacker.

For 99% it was player with removed sound files and building files.

You were killed by player that had removed structures and possible sound files.

See:
http://feedback.dayzgame.com/view.php?id=5683

Invisible zombies are brought to server by players that remove certian .pbo files (zombie files).

Part of the issue of this:

http://feedback.dayzgame.com/view.php?id=5683