Let's look at this question by looking at affirmative action, the university setting, and your role in it:
It's hard to gauge his specific position, but being against affirmative action/outreach programs does not mean that this person is against the group that is supposed to benefit from these programs. It can simply mean that this person sees affirmative action as the wrong solution to an issue that might or might not be an actual problem.
For example, this person can think that the gender of a student should be irrelevant, and they themselves have no preference for, e.g., male or female students. In fact, they do what is ostensibly desired -- they treat men and women the same. Interest, persistence, grades, performance, etc. should count, not whether this person is/identifies as male or female. They might even welcome women if they have similar competence (a requirement for the contact hypothesis to work). They might see the differences between the percentages of men and women in certain domains within STEM due to a different distribution of interests, not due to discrimination that requires affirmative action, or think that Academia is not specifically hostile to women but hostile in general (many PhDs, few tenure track positions). There is also the counter-intuitive finding that affirmative action might hurt those it should benefit. At least for race there was an interesting "intelligence squared" debate.
In the following, I'm assuming that this person has thought about his position.
Now let's look at affirmative action in the university setting. Unfortunately, some people think that anything but (at least) 50% women in highly prestigious fields like STEM indicate discrimination (ignoring, e.g., prior interests). And for some, it's an ideological issue where questions or an open debate with arguments based on theory and evidence are not tolerated. If you are not for positive discrimination, you are seen as acting actively against women -- even if you just apply the same standards to men and women.
Even worse, I get the impression that some universities get more and more infected by ideology. They are turning into indoctrination places where having the right (or rather: the left) point of view is all that counts (FIRE is an interesting source here). Personally, I think that universities can and should do better. If you cannot discuss "potentially controversial views" at the university then where can you discuss them? But realistically, in some universities open discussion of controversial ideas can draw a lot of outrage (including from students).
Your Role as 'potentially concerned person'
Given the explosive nature of the topic for many people, exposing a contrary view of someone could cause damage. Not necessarily because of the issue, but because you make it an issue. Especially if it is done without this person's knowledge. Or would you tell him in advance that you translated or summarized his postings and gave them to his prospective employers because you were "concerned"?
If you inform his employers/colleagues, I would hope that they have even a shred of integrity and have a look (and a translation) for themselves. Depending on how thought out his views are, they might conclude that he is not the problem but the informant is. They might even regard the informant as a backstabbing snitch who is envious that their new employee was accepted to "a very prestigious university" despite (what the snitch considers) his "potentially controversial views". Even if it damages his career (which it easily might), I don't think that the snitch would come out with a good reputation.
If the new post-doc on the other hand is open about these issues, good. I hope so. Issues should be discussed openly. But considering how easily criticism of a publicly widely accepted view can be misunderstood and misconstrued, it's his decision whether or when and how to talk about it in an Academic context. Personally, I do not think it would belong in a talk with a prospective employer as the topic is too complex and explosive for a superficial conversation and is likely to be misunderstood.
A better solution
If you are "really concerned" about his views, then you can -- as others have written -- talk to him. Discuss the issue with him on the platform of his choosing (here: Facebook). Of course, the same ideologues for whom affirmative action is "not debatable" might regard any person having a debate about the topic as a problem. At the very least you consider something debatable that for them is a no-brainer! And how would you react if he made a point? But perhaps that's a bit too much "censor in the head". ;-)
But if affirmative action really is a no-brainer, you should be able to argue for your point of view and try to convince him. Because frankly, no view -- even if it is/were "right"/"true"/"correct"/"the best solution there is" -- should prevail just because those who have a different position were stabbed in the back when it came to hiring and promotion.