HaKatan,
You asked for Gedolim who authored universally accepted seforim who also held that Zionism was not avoda zara. Here are a few (not previously mentioned):
R’Eliezer Waldenburg, the “Tzitz Eliezer.”
R’Reuven Margolies, author of “Margolies HaYam” on Sanhedrin
R’Tzvi Pesach Frank, author of “Har Tzvi”
With regard to the “oaths” the simplest answer is that the oath is battul because the League of Nations/United Nations/British permitted the state. This was the position of the Ohr Sameach.
Another simple answer is that the oaths are part of an Aggadata gemara. They are not brought down in the Rambam, Tur or the Shulchan Aruch. They are therefore not l’halacha.