Ofcurse, an editable poly should work perfectly fine.
The render looks like it has a big plane crossing at ground level thus the vrayplane question.
Some more sugestions: do you have turbosmoth with 0 iterations for render and the edit poly on top of it? Have you tried to do some isolate renders to find if there is any problematic object? Can be a displacement problem ? (Sometimes I forget the default max displacement cheked and get weird geometry…)
I seem to remember a bug that a hidden vray plane didn’t actually hide but it’s been a while since I’ve seen that happen and I know it doesn’t do this in the latest vray version.