I don’t think it’s illegal. The Strata Committee is usually empowered to act on behalf of the owners corporation (with specific exclusions). Application for a statutory appointment can be made by individual owners – even the Tribunal Member can just do it off their own bat if they think an owners corp is dysfunctional enough.
Individual owners can also challenge the appointment, but it would have to be on the grounds that it was unnecessary or that the original applicants were seeking some kind of material gain. Arguing that it was invalid because of an arcane point of law will get you nowhere.
Also, the Tribunal Member must have had good reason for allowing the appointment – they don’t just hand them out like lollies.