Hello Foni
Thank you for your inquiry.
No, you do not need a General Abonnement for the Saver Day Pass. This day pass is also valid for tourists. Only to note is that you buy it, with your right discount (reduced price with the Half Fare Travelcard or full price without the Half Fare). The route from Zurich HB to Grindelwald is included in the GA travelcard. At sbb.ch/travelcards you will find the area of validity at the bottom right under downloads. You can see there on which trains the ticket is valid.
Have a nice day.
Kind regarts,
ZoeS