Does Entity Translation hijack i18n's operations? I'd ideally like to use i18n to handle backend translation but use entity translation to maintain multiple language versions for each content node. 

Does this require a lot of extra work or lead to caveats? I'm hoping they just handle different sides of the translation puzzle.
It's not that difficult or complicated, you just need to know what to do, where and using what. Have a look at Drupal 7 Multilingual Sites book, it has pretty good explanation of the whole process. Essentially, yes, Entity Translation plus i18n modules would take care of most of the things for you.