benignuman,
Religious Zionism, striving to “gain and maintain sovereignty in Eretz Yisroel as a religious obligation” is not held as being in force by any major gadol to justify violating the oaths. Aderaba, it’s a severe violation of the oaths. Again, even the Zionist Rabbis struggle (futilely) to explain away the oaths.
Regarding after the state was established, there is no reason to believe Rav Elchonon would have held any differently except, like gedolim other than the Satmar Rov did, they joined in the State to save what they could from within. But, as Rabbi Resiman wrote, it was only the tactics that changed, not the ideals. The oaths were still in force and were being violated by Zionists.
Outside Zionists, this is universal, not “just” the Brisker and Satmar Rabbanim.
Zionism and the State were and are a terrible aveira and, besides that, a horrific disaster.