yes. The leading underscore for private and protected is the legacy coding standard used in Doctrine 1 and inherited at the beginning of Doctrine 2 development. We then decided to stop using this legacy rule but 2.0 was already released as stable and renaming protected methods would be a BC break.
All new code avoids them unless it is mandatory because of inheritance from an older class (and reworked code is regularly renaming private properties and methods, for which it is not a BC break)