I'm not sure, but you may have to set c.v = NULL; before ent_setvertex or alter the normal vector of c.v manually.

it works:

// after c_trace
c.v.nx = (float)hit.nx;
c.v.nz = (float)hit.ny;
c.v.ny = (float)hit.nz;

because to write you need c.v:

d3d vertex struct c.v.*:
typedef struct {
float x,y,z; // position
float nx,ny,nz; // normal
float u1,v1; // coordinate set 1, for base texture
float u2,v2; // coordinate set 2, for light map or detail map
float x3,y3,z3,w3; // coordinate set 3, for tangent or other purposes (A7.06 and above only)
} D3DVERTEX;