Rav Chaim Kanievsky fully supported them as does almost the full gamut of Israeli charedi gedolim.
SOURCE ? Other than shmuos from R' Chaim I do not think that any Israeli Gedolim publicly supported them. This was considered to be damaging for degel enough that they had pesach lerner go on the israeli radio to say that degel has nothing to do with them and any help he had from Pindrus was just as a personal freind.
I love how the anti-group was super quiet when eretz hakodosh got them all permits to get all the american yeshiva students into the country during covid. Suddenly they all took the entry permits and gave full support to the group.
At the time there were many people that were very upset at them because they did not accept the claim that the government would not have otherwise allowed the americans in ,rather the "IGUD" just got themselves in between the yeshivos and the misrad hapnim .The yeshivos were forced to work with them (
for a hefty fee) because there was no other way to get a visa. Some believe that if they hadn't gotten themselves involved things would have been much simpler.
The same heter allowing to vote for Gimmel etc applies here.
Its a completely different shaila with many differences . One difference is that by elections for the government you have a government that is controlling much of the citizens life whether they like it or not and the shaila is whether or not to get involved to save what you can. As opposed to willingly signing up as a member of an organization in order to be able to steer some of their funds towards your interests and away from the interests of the reshaim.
Another significant difference is that in order to sign up for the wzo one has to sign a declaration that has aspects of kefira in it .No such declaration is required in order to vote for the knesset.