<p>I've got a bunch of 3D vertex positions &amp; need to generate a convex hull containing them; does anyone know of any QHull bindings for .NET? or native 3D Delaunay triangulation algorithms?</p>

A 3d delaunay is tricky, I'm not sure it's even possible to strictly define a delaunay constraint for a 3d surface.
The normal technique if you just want to mesh a surface is to pick a direction and map that onto 2 coordinates and do a 2d delaunay. For a height map it's easy to just use x,y.
Then when you have the nodes forming each triangle you can of course use their 3d coordinates.
The best 2d code is probably
http://www.cs.cmu.edu/~quake/triangle.html
This will also give you the convex hull