I think the shaman is there to symbolise the passing of the old order, especially as he is killed by a revolutionary: a sign of the times, with religion being stifled and not permitted.
This is someone who would carry enormous respect among his people but what do they do with his body? Take it down to a dank chilly basement and lay it in a nest of junk. It is the death of spirituality. Without that, the place truly is moribund.
He strikes me as being someone who is genuinely in touch with the spiritual side as well. Matula is searching for it, maybe, but has no idea how to respond to it - chain the shaman like a dog in his kennel! - but he fails in his objective. The shaman escapes him: "The keel slides through the mud and floats free". I suppose I am totally contradicting myself here, but perhaps this is positive: that the spiritual can't be confined, trapped, in the end? I kind of think the shaman dying and passing on to another plane, as it were, is the heart of the book for me. The central characters have lost their way, their spiritual way, I mean, and each of them, to a greater or lesser degree, maybe, has their moment of enlightenment, and their chance to move forward.
Edit: Depputante, the albino mentions the deer on p265.
"Luck... inspiration... both only really happen to you when you empty your heart of ambition, purpose, and plan; when you give yourself, completely, to the golden, fate-filled moment."