United MileagePlus (Consolidated) - Can I combine intineraries?

I have an award ticket from LAX-ICN-SYD-ICN-NRT-LAX. LAX-ICN-SYD-ICN are on OZ and the final leg ICN-NRT-LAX is on UA.

On either side of the award ticket, I have a separate paid itinerary from LAS to LAX and back, on UA.

Can I combine these 2 itineraries into one? I am asking for baggage and checkin purposes.

No - this isn't possible. You may be able to get your bags checked through at each end by presenting the checkin agent with the details of the other booking (this is called interlining), but they will not be able to check you in on the onward flights.