I'm sorry to report that creating and loading an esp that modifies the Hammerfell worldspace did not work for me (could see the land in the cs just fine though). There was still no land at all, just those rocks. And what great rocks! The models for those barrows are absolutely gorgeous!
I just was pasting in my load order in this post when I had an idea: I remember hearing about the SIlgrad Tower people encountering a bug where the ESM had to load second, right after the oblivion esm, for the land to appear. I moved the two esms right to the top and took a peek and voila! IT WORKED!
Why this happens I couldn't say though. My understanding was the ST people eventually found a way to fix it.
Okay now to go play the game!
Edit: OK Lady Neravar, looking back at your post now, I understand what you meant. At the time I read it as just making sure TR_OoT_Main loaded before Hammerfell.