And that is my point: they are already certified by their respective religions. The catch here is that other Army officers or soon-to-be officers begin wearing their branch insignia when they are "branched," not when they graduate OBC, as in this excerpt from
http://www.norwich.edu/about/news/2005/branch.html-- "One by one, each cadet was called forward and asked to stand in front of the audience. An ROTC instructor then came up and faced the cadet while his or her branch was announced, before pinning on their insignia. For many, the moment prompted a huge sigh of relief." A similar scene happens in OCS.
Why should it be any different for the Chaplain Corps (other than because the Chief of Chaplains wants it that way)? If it is a matter of saying, "Well, the current chaplain insignia isn't branch insignia, but rather religious demonination insignia," then I say to that, "Pshaw, that's only semantics." Of course, this all probably owes to the fact that chaplains are considered professionals prior to coming in, so they have a different training pipeline and different status during their training than typical officer candidates or cadets.
In this day and age maybe all chaplains should wear this new insignia, considering wearing religious paraphenalia can be considered offensive by others...and the US Army is all about being inoffensive.