c_updatehull is normally not required after ent_setvertex, except for the cases mentioned in the manual. Otherwise the engine calls c_updatehull itself when vertices are manipulated.

ent_fixnormals is not required either, because it doesn't do anything with terrains. It's for models only. Thus, the normals of terrain must be set manually through the nx/y/z values. It would make sense to implement fixnormals for terrain also - in fact I see that it's already on our list.

Calling a function with a wrong argument, such as 0 instead of 1, normally doesn't matter as this is internally corrected. But better look in the manual and use the correct value.