Not sure if it's the case for all vintages of Zon's, but indeed the fretless & fretted ones I have (both that way from inception) seem to have the same fingerboard material, and both seem very similar to rockwood/diamondwood that I have on a couple of Greg Curbow basses. Not sure if it's precisely the same supplier, but looks very similar.
If the fretline-installer was competent, I see no reason why the lines should be "off" of where you'd put frets, but it should be relatively simple to check? Perhaps use something pointed/sharper than a finger & depress the string on the fretline...
Curious to hear how this pans out

Good luck!