2. Slava is surley Christian tradition since it is practicised exclusivelly by Christians (some of them are nominaly, but nevertheless they use that fatc to confirm their nominal adherence to Christianity). There are 4 theories about origin of Slava, two see it as something derived from non-Christian practices, but no matter of origin, Slava is family celebration of patron Saint, in Christian spirit, with Christian aspects, with Christian prayers and chants, with Christian symbols (koljivo, hljeb, vino). Being derived from something is not sam with being that something. Besides that there are theories about pure christian origin of Slava, and they are better founded.
1. Someone who teaches comparative history of religion on the Faculty of Theology, is an expert on comparative history of religion. Furthermore it bears more scholary value, because he didn't solely see it from a Christian mainstream perspective.
2. Yes it is Christian, since no pagans exist. Yes it is better founded since no pagans exist. Second, I do not know of any other Christians than Serbs (and maybe some groups bordering them) that celebrate the Slava, therefore I doubt it is of Christian origin, founded in the Semitic culture.
P.S. I personally believe a lot of Christian practices, are of pagan origin. I would go so far to say all of them, except the ideal of monotheism.