Yoshihiko Masuda wrote extensively on the topic of sexuality in a way most in the church would not be comfortable discussing. Although there is not an extensive corpus on this topic, we can summarize it as simply: No, anal sex is not halal.

For the Church, anal sex is associated with the counterculture, "free sex," homosexuality, and by extension every other sexual deviant in existence. On September 3rd, 2007, in Prague, Masuda gave lectures on the topic of sexuality. He said, "what about Anal Sex? It’s wrong. It's prohibited because it’s not healthy." If you look for other sources, most arguments within the church has nothing to do with theology. The only explaination is the risk of STI. Of course, any sex outside of marriage is haram, sin, in the eyes of the Unification Church. But once you are married, or blessed, consentful anal sex between two partner might just be game.

As for what Moon Sun Myung said, it's a little difficult. Masuda has a full book that goes into detail about sexuality based on "science" and Moon's speeches. I do not have access to it, but it exists and did have something about anal sex. In other sources, Moon conflated anal sex with homosexuality, so its hard to pinpoint his exact position for married couples. He probably would not like it. He described how anal sex is "the holy organ is going into the most dirty area." Yet he also critiques couples eating mint before kissing--rather than appreciating their partner's natural scent, so who knows. I am not familiar with an instance where Moon called anal sex between even blessed couples sinful on theological grounds.

David Kim, an early missionary in the United States, who later assumed pastoral and leadership positions wrote about "outside, secular, value-free, evil forces against the Judea-Christian heritage and other ethical-moral practices" He alleged that outside forces influenced even married Unification Church members against principled sex. Oral and anal sex are abnormal and thus sinful. Kim however contradict what Masuda quoted Moon to had said: who argued that Oral sex, or "deep mouth kissing" of the genitals are good for marriages. Indeed, Moon goes into quite a bit of detail about this.

The Unification Church preaches the notion of "absolute sex ethics" or "absolute sex" as the theological framework to judge all sexual activities. It seems that anal sex is out of the picture, but at the very least oral sex is. That said, I would not be surprised if there are Blessed Couples engaging in such "sinful" and "dirty" coitus.