If we are talking grass/shrubs, then there must be a way to detect them since the player can crush them under his weight
The grass clutter is not placed on the terrain when the terrain is created but it's actually defined in the config so that you define on which kind of ground texture a particular clutter type appears, so it's basically procedurally generated when you load up the terrain (or the "typing" is for the streaming, what ever).
So the clutter is not even a regular map object.
Bushes are a different story since they have to be placed on the terrain while creating it thus being normal map objects.
However, there really is no named properties or config values that would define the clutter to react with the player so I'm guessing there's some hardcoded engine thingy making objects with certain name to be treated as clutter (all the clutter objects are named
clutter_****.p3d) or something.
Basing this theory on the fact that I have clutter on the terrain I'm developing that doesn't react with the player and the clutter model name doesn't start with
clutter.
Detecting the clutter would not be a fool proof thing even if it was possible because if you turn the terrain detail low enough the clutter disappears..