I don't know what creating supersoldiers have to do specifically with a xenophobic empire, and rather with a militarist empire. Anyways, genetic manipulating can be used for much more stuff.
Most other cases. It would be sort of weird if one ethic and not its counterpart had an ascension path, and if you don't have any of the three ethics... I bet the genetic path is the generic path, allowing you to pick a path even if you lack spiritualist or materialist. You could always of course pick neither since they apparently needs to be properly focused on, but always having an option helps.