Yes, BlueTEC is just Mercedes' name for the DEF system that treats the exhaust. There's nothing special about the engine itself, the exhaust is just treated.

BlueTEC is just a marketing term like SSRS ( airbag ).

not as much ... Bluetec is just an advanced catalytic converter, that reduces NOx. Mercedes has been implicated in the emissions scandals, afaik. Inherently diesel is less refined than gas, so it does not burn as clean.