Whether a particular external DVD player works with Apple's DVD app seems to be down to the USB chip in the DVD player. Data point: I removed the DVD player from my MacBook Pro to make room for a second hard drive. I bought a cheap $2 external DVD enclosure for the DVD drive from a Chinese no-name manufacturer. It does not work with Apple's DVD app (but it does work with other DVD players like VLC), even though it's an Apple mechanism.
Stick with name brand external players with good USB chips and you'll likely be fine, but be sure you can return it if it doesn't work. Cheap external drives from dodgy vendors, on the other hand, are more likely to be problematic.
