In the description of Elemental spirits in the Animism chapter, the book says that the shaman can embody the elemental spirit. In doing so, the shaman will gain the abilities of the elemental.
From the Animism chapter:
[Embodying the elemental] grants the animist the physical and magical benefits of an elemental...
The animist's STR, DEX and Hit Points are replaced by the spirit's values...
From the Elemental creature entry:
Elementals are naturally immune to magic that is based on their particular element... Neither can they be injured by mundane weapons, as their physical forms merely replenish material from the immediate environment...
Does the animist inherit the immunity to physical damage?