In a nutshell, no, the combination of the two passes is not sufficient for your journey.
The German Rail Pass is valid from/to Lindau (D). The Swiss Travel Pass is valid from/to St. Margrethen (CH). As a result, you will need an additional point-to-point ticket from St. Margrethen to Lindau.
A seat reservation for the entire journey is advisable as, from my personal work experience, these trains are always well booked. You can get it, as well as the additional ticket, from the SBB Travel Center in Winterthur, for example.
German Rail Pass: Unlimited train travel in Germany | DB (bahn.com)
Swiss Travel Pass | SBB
I wish you a nice journey.