Radiant in strange indeed when comming from another 3d app. if does things very diffrent. I too came from another 3d app to the worls of radiant and i took som egetin gused to fore sure..
Im not 100% sure, but afaik you cannot make a map in blender or milkshape or whatever and then turn it into a map in radiant. What i know you can do is make models for your map in a 3d app and then export them to a sutable fileformat (.ase, .mdl, .md2, .md3) and import them with the misc_model entity in radiant. Thise models are not limited to status or trees, thay can be enything from stones to bridges and ufo's. but models are not solid, so they will need to get clipped of if the player can toucs / shoot them. Also a map cant be made up of only models, you need some solid "brushes" to make up the main hull of the map.
Radiant is not the only option for nexuiz mapping, eny exiting sftware capable of outputting quake3 bsp will work. The ones i know of that can do this is: GTKRadiant, Quark, gmax. There may very well be others too.
I would howerver recomend that you do give radiant a try, its the most commonly used quake map editor out there and for this reason there is alot of information available for it on the web.
HOF:
<Diablo> the nex is a "game modification"
<Diablo> quake1 never had a weapon like that.
<Vordreller> there was no need for anything over 4GB untill Vista came along
<Samua>]Idea: Fix it?
<Samua>Lies, that only applies to other people.