Regarding Trees LOD in fallouts. First please read TES5LODGen description page on how LOD works in Skyrim since it inherited Fallout's LOD and they are very similar.
Trees LOD in fallout has slightly different naming for files
meshes\landscape\lod\<worldspace>\trees\<worldspace>.*.*.*.dtl those files have the same format as *.btt in Skyrim
meshes\landscape\lod\<worldspace>\trees\treetypes.lst, also the same format as in Skyrim.
But the last difference is a nail in the coffin, atlas file holding flat images for trees lod in a worldspace
Yes, there is no worldspace name at all, it is a hardcoded LOD texture for all worldspaces in the game. The only "difference" is if worldspace editorid starts with "DLC4" game will use textures\landscape\trees\treeswamplod.dds, and this is hardcoded too (hello Point Lookout).
LODGen for trees builds atlas itself from separate LOD images of trees used in a worldspace. Since the atlas is common in fallout, trees LOD must be built for all worldspace at the same time. I just don't want to do that honestly, this will make running FNVLODGen a mandatory when any tree is changed in any worldspace in the game.
Unless you have contacts with people who can reverse engineer engine and create NVSE plugin to override used atlas texture name for worldspace similar to Skyrim one, like textures\landscape\lod\<worldspace>\trees\<worldspace>treelod.dds and fall back to default procedure of atlas naming if this texture doesn't exist for the current worldspace, I don't see any point in doing trees lod for fallouts at all. Only objects LOD will be generated by FNVLODGen for now.