I'm not religious at all myself, nor am I an anthroposophist. I have two Waldorf "lifers". One is atheist, and the other has a kind of amorphous religious belief, without following any particular religion. If your husband is concerned about stuff "out there" on the internet that Waldorf secretly indoctrinates students about religion and other such, it's pure nonsense. The internet is good at boosting the mileage for kook rumors and legends. It's not hard on the internet to find every kind of "so and so knew so and so and they said such and such", and the tale can even have an element of truth to it, but would generalizations also necessarily be true?
But Waldorf is not a strict separation kind of education either. For people who are offended by themes, references, traditions or people which can be identified to religion or a particular religion (and I think both religious and non religious people are pretty touchy about these things today), it can get complicated. Waldorf schools say blessings, they learn stories from the Bible and other religions, and in the early grades, there appear these "magical" beings in the play and pageantry, such as angels or gnomes.
If your husband is okay with this, and is more or less worried that his child is going to be converted or that there is preachy stuff going on in the school, that's very, very, very unlikely. But we all have our own yardstick, and what makes me cringe is different from the next person. I have no problems with school regarding their handling of Buddha or Moses, the angels, and so forth. Just take my son, the atheist. A lot of his favorite books have religious themes; he's loved the "His Dark Materials" series, for example. But he is cringing his way through one of the books he was assigned to read for this class he's taking for extra credits at another school--not Waldorf; the book is more like a personal religious "testimonial", one trying to persuade readers toward religious faith. He views the former books as "literature", the latter feels to him like an "intrusion".