I don't see why you couldn't make rocks in Doom 3 the same way you do in Quake.
When you're finished, turn the entire terrain into a func_static and turn the simple room around it into caulk.
For parts that the player can't interact with, there is some key that lets you make the func_static nonsolid which supposedly saves RAM because no clipmodel is needed (I think).
You can then export the stuff (obj) and tweak it in Blender all you want, but for rough terrain, just to get the rough outline and scale, I don't see why you wouldn't want to use triangles or patches. Just to approximate it in the editor and get a feel for it.
You asked me to share my expert doom 3 mapping knowledge (lol) so here is other random stuff I found out while mapping:
- Shaderparm7 is used to set green/red lights on the door frame models. 0 is red, 1 is green.
- I ripped the frame and door models from id maps and tweaked them to my needs. All the doors are models as far as I can see, so are the matching frames, all nicely on the grid and on the Z point. The glass inside some func_doors is a func_static hooked up to the func_door with the "bind" key, like "bind" "door1". This makes the glass follow the door's movement in a master/slave way.
- Like Necros said, two ways to make consoles. a) models (in the mapmodels/com folder I think, look at the communications map - com1 or similar); b) brushes for the straight parts, patches for curves, small brushes for the guis.
- GUIs: For the model consoles, keys gui1, gui2 and so forth point to the gui files... for handmade guis, simple patch mesh turned into a func_static with common/entitygui texture and placed roughly 1 unit in front of the physical screen, can target stuff it should activate and "gui" points to the gui file like guis/comm1/sentrybot.gui is the panel that says "Activate sentry", for example. There are a lot of those.
- Mapmodels can have different skins; for example, skmachines/skcube.lwo can have "skin" set to skins/skcubedirtred to create the red version of that thing.
- Sounds are placed in maps using the speaker entity.
- Glass is simply a material.
- Two ways to make sky: a) like in Quake, slap one of the sky textures on brushes and b) portal sky, still looking into this last one.
- Lights; brightness results from the size of the light volume, as well as the color, where white is full brightness. You can assign textures to a light source, such as "texture" "lights/xray02".
- Entities under "movable" are physics objects, these drop to floor automatically. So do monsters, but not weapons for example. You need to place the weapons and ammo in the position you want them to appear.
- Decals are put on simple patch meshes of the desired size and shape and placed roughly 1 unit above the surface.
- Textures can be resized pretty freely without looking bad, so you don't have to build gui screens or decals at a certain size. Rather click "fit" in the surface inspector.
- The scale of everything is comparable to Quake, so is step height etc.
- You can load different mapmodels by creating a func_static and choosing models/mapobjects/whatever.lwo (Radiant will pop up a file browser).
I'd be interested to exchange testmaps and knowledge, hit me up on irc maybe.
http://kneedeepinthedoomed.files.wordpress.com/2010/09/sotox2.jpg
http://kneedeepinthedoomed.files.wordpress.com/2010/09/sotox3.jpg