An Easter sunrise service might appear to be "an obvious pagan celebration," but it bears mentioning that the Resurrection stories in all four gospels indicate that Mary Magdalene and others went to the tomb very early in the morning to anoint Jesus' body. Indeed, the King James Version of the Matthew account says specifically that it was "as it began to dawn toward the first day of the week," and the John account says that it was "yet dark" when Mary Magdalene arrived at the tomb. Therefore sunrise services are also in keeping with the Bible stories, regardless of any pagan precedents.
(I have to quote from the KJV because I have only a KJV New Testament at hand here at work.)