Did some research. The Australian DVD is 1.85:1. But the review on the US DVD from dvdtalk.com say that 1.33:1 is the OAR. So I still don't know which is right.
I have the US region 1 DVD of Harvie Krumpet and can confirm that it is indeed widescreen (1.85:1). I have seen some misinformation on other sites about it being a full screen DVD but it is not. Since there is no information about the aspect ratio listed on the package some people may be making the assumption that it's full screen. DVDTalk has a review that confirms it's widescreen. So does the TowerRecords.com site.