Many students have asked me for research tips about Zainichi Korean society. I read some of their papers, too. It occurred to me that some of the most basic things are not as obvious as I thought, and I am repeating myself in my comments. So I may as well share some of them here.
As often said, Zainichi Korean society today is very diverse. I am not even sure if "society" is a fitting term to describe Zainichi people any more. You will meet Zainichi Koreans of all sorts of identities, occupations, and backgrounds in Japan. But even then, major groups and gatherings still have some connections with one of the two organizations, Chongryon (Sōren 総連) or Mindan 民団. This might not be obvious because most of them do say they are open to all Zainichi Koreans (and they are indeed available to all Zainichi Koreans). The first step to identify groups' general orientations is to look at their names and see what letter or word they use to describe "Korea."
「韓」 means South Korea, 韓国. This usually indicates a stronger identification with South Korea and/or Mindan.
「朝」has a little more complicated meaning coming from the term 朝鮮. It is supposed to indicate the entire Korean peninsula. Many Japanese tend to avoid the word 朝鮮人 (Chōsenjin), however, because the sound of it reminds them of the derogatory use of the word widely seen in Japan's modern history. But Chongryon people take pride in being 朝鮮 saram (person), and usually use the letter 「朝」. If you see 「朝」in the group's name, by the fact the group did not choose「韓」and is comfortable using「朝」, it most likely indicates a Chongryon-leaning group.
Note: Many academics with no political commitment to either side also use「在日朝鮮人」especially for the history up to 1965.
「在日韓国朝鮮人」is a phrase that scholars often use to describe all Zainichi Koreans.
「コリア」(or コリアン) is a word people (especially outside of academia) use to go very explicit about not favoring one regime over the other. That does not mean they are "neutral" though--some of the Japanese rightwing groups use 「コリア」, so you still need to figure out their orientations from the context and members.
This rule of thumb might not apply to businesses. Even Chongryon people might use the word 韓国 when it's more marketable. I am only talking about non-profit gatherings.
If you try to reach Zainichi Korean people or groups in Japan, you might find a bigger representation of Chongryon or Korean school graduates. Many Korean-descent people have switched their nationality to Japanese and do not necessarily associate themselves with other Zainichi people any more. Then those who are visible and reachable tend to be self-identifying Zainichi Korean people. Korean school graduates have greatest confidence and visibility. They also have a network built in the schools. If you are conducting a survey with random sampling, pay attention to the proportion of Korean school graduates and analyze the results accordingly.
If you are interviewing Zainichi Koreans and you are not sure which word they use, you might want to start by using "在日コリアン" and see what they use, or ask them which term they use most comfortably. To some people, the differentiation is very important.
I wonder if it is Pachinko that is increasing inquiries about Zainichi history sent to me.