Oz uses the PAL TV system so in that sense no worries. Be careful regarding In-game downloads though. If you have a UK version of a game and try and buy extras In the game in Oz, that may not work. That happened to me when when(unknowingly) purchased a U.S. Version of a game and the extra stuff I downloaded on the PS network would not appear in my game even though the download seemed fine when in progress of doing it
US/Eur/Jap versions of games have a different SKU/product version which trophies/save games/DLC are linked to so they are not interchangeable.
Online games usually have the same NP id so you should be able to matchmake ok.