Hi Richwest,
I'm sure you could use World Machine to make fabulous terrain. I'm not sure about the export options in World Machine, but if it won't export in a file format that can be imported into ArmA, then you could always export it in a format that can be read by L3DT (e.g. TER), and then export from L3DT in a format that can be imported into ArmA.
Cheers,
Aaron.
PS: I split your post into its own topic, since it had no obvious connection with that
two year old thread about a resolved Grome importer bug. Your question also doesn't seem to have much to do with L3DT, so you may have better luck getting a knowledgeable answer from the
World Machine forum or from an ArmA modder forum.