You can remove grass and tree and any other object, in the old fashion way, coz the signatures aren't enabled (yet) on the servers. Plus VAC shouldn't care about it, since it is a mission modification (legit) and not memory manipulation:

\SteamApps\common\DayZ\Addons\

to remove the trees and grass, remove/move:

plants2_bush.pbo
plants2_cutter.pbo
plants2_misc.pbo
plants2_plant.pbo
plants2_tree.pbo

...you can remove any other building type in the same way.