Hello,
for what i have read and heard the swastika is indeed an ancient indian symbol for the rising sun, and it was used mirror-inverted by the National socialists. The word "swastika" itself comes from the sanskrit, and is used in hinduism and buddhism religion. Since the celtic tribes derived from the indo-european peoples the swastika remained a symbol that was connected to the rising sun, fertility and what not.
As an old german ornament the swastika was rediscovered by german national movements at the turn of the century. A lot of jewish people were as nationalistic as their protestant and catholic compatriots and also used it. Jewish people had of course fought for their country as soldiers against the Entente, and a Bavarian squadron in palestine had helped the jewish population against attacks and pillaging of some arabian tribes.
There were "certainly" people who already believed in a "jewish world conspirancy" before the 1930ies, also in England and the US (e.g. Mr. Ford).
The "Freikorps" in Germany recruited from all kinds of people, often fighting against each other for power, not only against the red. The situation in Germany was a mess after the war, due to all kinds of problems. The mirror-inverted swastika ("Hakenkreuz") became the symbol of the national socialistic party banner in 1920, and later the political symbol of the Nazi regime.
Greetings,
Catfish