ATM it doesn't seem like it's possible to do scripted orthographic renders in Keyshot. Or at least I can't find an API to do so within https://keyshot.com/scripting/doc/6.3/lux.html.
You can set do setStandardView(lux.VIEW_ISOMETRIC) on the camera but while this will set isometric viewing angles, it will not set the projection type so you'll still get perspective renders.