You need to define what do you mean by “Zionist”? Members of Hashomer Hatzair – probably not. Supporting Jewish settlement and later state – probably many. Also, note that sometimes fierce fighting happens between leaders trying to bring people to join their movement at the expense of the competing movement – does not mean that they always disagree. If you look at recent discussions here, you will see that, say, Netziv, Ohr Sameach were not at the same position as others.
As to general “yeshivos”, we might have a very idealistic view of what was happening there. for example, at some point Telshe yeshiva was emptied out because all students became socialists, so Slabodka sent new students there …
As to YU, I am not sure whether there was politics involved when R Moshe Soloveitchik (son of Chaim Brisker) was there in 1930s, but R Moshe was already involved in creating modern religious schools when in Poland in 1920s. His son, R YB Soloveitchik was of course a supporter of Mizrachi, with some reservations and had explicit goal to produce Rabbis who could work with Jewish communities that had Americanized and educated people. His observation from talking to college students in 1950s that they had a lot of questions that they were not able to get answered either from reform or from Rabbis who did not know anything modern. So, it is R Soloveitchik’s “fault” (as well as Lubavitchers) that there are observant Jews outside of Boro Park – without their efforts, everyone would be assimilated already and you will not encounter such posts on YWN.