Yup, that is fine. Really hard to find a bad copepod, they are almost always good to have and really can't have too many in a tank if you have a mandarin. Some amphipods are bad and isopods are the worst. When I add copepods I have a sump to put them in, but without a sump I would try and use a turkey baster and gently blow the copepods into the rocks as deep as you can get so they have a chance to hide and multiply. If you simply pour them on top of a rock not nearly as many will make it.