I used to use my 2002 Powermac G4 to convert non-U.S. DVDs to region-free copies for viewing at home. When I tried this with my 2009 Mac Pro, there was no way to bypass the DVD drive's automatic region check. Even if I bypassed the running of the DVD Player and went directly to VLC (which will cheerfully run any region's discs), it would no play video on the Mac Pro, as the drive refused to serve the data. The external superdrive that I use with my 2010 Macbook Air, on the other hand, works like the 2002 machine -- if you bypass DVD Player, you can watch the video with VLC and convert it to region-free content if you like.
My question -- is there any way to know how a given machine will treat non-local DVD content other than trial and error?