I don't seethe problem with it. Your DH is a catholic. It's not as if you are completely changing religion to get into a school.
As parents, we have a moral obligation to do the best for our children, and if that involves the next 2-3 years, every Sunday morning, then so be it.
A couple of points up the thread, our Catholic secondary's have between 33% and 25% of places to non Catholics, they go on the usual criteria - looked after children, siblings, other religious observants, then the non believers.
As for baptism to get in, if you are white, native English speaking MC you stand a better chance than a child from a Polish family. Also locally our catholic schools are mainly West African children, they are either Catholic or religious observants - not a naice middle class amongst them. And the other places are East European, either Catholic or Orthodox. Odd how the dreadful snobbery manifests on MN, so many stereotype come into play.
People generally want their children educated like-with-like in the same way over my dead body did my children go to the school populated by 'erberts from the local sink estate where drugs and knife crime are rife. I want my children to broadly mix with people with my values and outlook, this does not mean they had a restricted social mix.