The trams look like Duewag GT8Z and yes, they were built as "Einrichtungs - Gelenktriebwagen" so for single direction traffic.
I have seen the new ones in service a few years (2012) ago, but do not remember if they are single direction or not.
Google maps shows the return loop after the Igls station.
I believe the 6 route from Igls to Innsbruck originally ran around the city centre loop but the current map shows it terminating at Bergisel to connect with route 1 to/from the city centre.
Both routes 1 & 3 have loops each end but the Igls route now seems to terminate at a straight line in Klostergasse in route 1's return loop: