So you're using darnui v04? If you are, follow gopher's recommended install procedure. There is not much difference in FNV and TTW when it concerns the hud, as far as I can tell. Make sure to use Darn's build, as it works flawlessly with oHud, using gopher's patch. I could never get Roy's update to work seamlessly with it. I don't think he got quite that far with it, what with people insisting it to work perfectly right from the get go, pipboy replacers and everything. So if you have ver .05b9 or 2.3 installed, I'd roll back to .04 if you wish to use oHud. Both of the new versions work flawlessly with just about everything else, it's just oHud and pipboy replacers that it has problems with.
This seems to be a bit of a sore topic with some right now, if I'm reading the atmosphere right. Just remember, if using .04, let oHud take control of everything, except for FlashlightNVSE, that means oHud gets to overwrite all files except for that mod. The DUI patch goes on top, and then UIO. Not that the install order of uio makes a difference as far as I can tell, as it scans your hud files every time the game starts.
Edit: It seems that 2.3 does work with oHud, if installed right, I just checked it out myself. So if you have that version, that's what I would recommend using.