I suppose it is fine to occasionally check the name on the Landgate site but as it is a copyrighted source you should not routinely use the info provided to update osm unless they have provided explicit permission to do so. There is a list of sources that can be used in osm here
https://wiki.openstreetmap.org/wiki/Australian_Data_Sources and you may a suitable source there. I expect others have already tried to obtain permission from Landgate without success.
If you feel that I am mistaken and I may well be as I am not from WA, then I suggest you ask the osm community on our forum or mailing list. 
https://wiki.openstreetmap.org/wiki/Australian_Mapping_Community
