So does this mean that the roster of A330 and A340 pilots is combined?
As far as I'm aware of, you are correct.
Just a rough example:
on the roster it may say you are to fly from HK to DBX and back in the A330, then later on that month (same roster) fly from HK to Rome in the A340 and back again etc
(the routes may not be correct but hopefully you get the idea)
I am not sure if you can get an A330 flight and an A340 flight in the same month, or how the crew scheduling goes in that regard. I can only say that CCQ'd Airbus pilots in Cathay are rostered to fly both on A330 and A340-operated flights.