We have had a few cases like this in our area over the last few years. In roughly half the woman chose to have her child taken into care to be with her partner/husband. I can't quite fathom it, myself.
How can social services not be concerned? This woman is described as vulnerable- exactly the sort of person who is likely to struggle to stand up to him and protect the child should he prove not to have been rehabilitated. Which may well be why he has chosen her.
The man was a teacher, who put himself in a profession where he would be in contact with children. Which gave him access to those children while in a position of power, authority and trust. That is quite a calculated thing to have done.
I can see the point that rehabilitation is supposed to give people a second chance. But it doesn't really cover a second chance at everything: he wouldn't be allowed to teach again- or hold any position where he would be required to work with vulnerable people again. Because the judgement is taken is that it is more important to protect these vulnerable people from the risk he might pose, than to give the offender a second chance.
Given that, I'm not sure that it as simple as he has served a 15 month prison sentence and now is magically rehabilitated enough to be a parent. I would have my reservations. Mainly as I'm not sure that something like sexual preference can simply be altered by a jail sentence plus possibly a "course" of treatment.
I think it possible that people can be taught not to act on their attractions, but I wouldn't want a convicted paedophile left alone in the company of my child in any capacity, let alone as their father. I can't see the risk being one worth taking.