So, I ran TES4LODgen and it kept freezing up while it was regenerating Tamriel. There were no error messages, it just stopped working. I thought maybe it needed time to think, Task manager said it was not responding, but I left it for a couple hours and nothing, so I stopped it with task manager. Tried several times but the same problem.

I did some research. Did not find much. I read on the nexus forum that TES4LOD gen can get hiccups from some of the TWMP landscape mods and I am running TWMP Valenwood Elsweyr. Unfortunately there was not a lot of detail about what caused the problem or how to fix it (other than deactivate the offending mod).

So, I deactivated TWMP Valenwood Elsweyr and tried again. TES4LOGgen ran like a charm, did its thing in less than three minutes. All works great, buildings are visible in game, etc., except that when I reactivate TWMP Valenwood Elsweyr, all the buildings that TES4 LODgen made visible are now gone.

Is there any way to make these two work together, or am I stuck with choosing between distant buildings and the beautiful jungles of Valenwood.

What version of TES4LODGen are you using? You can grab the latest version of TES4Edit and rename the executable to "TES4LODGen.exe" and it'll generate LOD data fine. Admittedly I haven't tried it with that mod that causes problems for you.

I am using 3.015 experimental. I read somewhere someone recommending to just change the name of TES4Edit but that sounded so weird I thought they were kidding. I assume I will need to rename it outside of my Oblivion folder before installing so I can keep a copy of TES4Edit there for cleaning and such.

Yeah, that's best. Create a new copy of TES4Edit (I'd recommend 3.0.31 myself, I had some problems with an earlier version and one of the UL's LOD generation since using this version I haven't had that problem) and rename the copy.