I encountered this error yesterday and I think I've figured out a workaround.
This seems to be caused by the custom menu that Prairie Fire DLC has. pixelW and pixelGridBase are functions that are related to screen resolution and I suspect one of them returns zero when no screen is attached, i.e. when using a headless client. This causes the zero divisor errors.
The workaround is to go to steam workshop and install a mod called S.O.G. Prairie Fire Vanilla Main Menu on your server. Launch headless clients with this mod loaded. This restores the vanilla Arma 3 menu and fixes the issue.