Can I use Adblock Plus for Android and still see per-app data use?
From my tests, data usage still show normal usage. E.g. using Firefox, firefox data usage increase, using Google+, Google+ data usage increase, etc... Also, it is not double counted for Adblock Plus. (I used ~15MB total, and Data usage report 340KB for Adblock Plus).

Tested on Android 4.1.2.