I think that your Owners Corporation (O/C) may be heading towards a mine field if it expects that any act or omission by its employee (whose role would be defined as a “caretaker ” in NSW) would absolve it of responsibility under any Legislation.
The caretaker and the O/C are separate entities, so, the former gets no benefit from the latter’s insurance cover. Consequently I believe that each entity must have its own insurance cover.
As to the nature and extent of that cover, even though the O/C may have effectively delegated some of its responsibilities (e.g. to properly maintain the common property) to its caretaker, both entities remain jointly responsible and should I believe hold identical coverage for all nominated activities where that joint / shared responsibility exists, including for workers compensation and legal liability (incl. personal injury, property damage, legal costs etc), and ideally with the same insurer to avoid conflicts should a claim arise.
The O/C should seek the advice of its current insurers re. the above, but before commenting further, could you please advise what State you’re in, whether the part-time building manager is also a resident (owner or tenant), and whether your Strata Plan is entirely residential or mixed-use?