If a source has the same name but gives a different type of bonus, does it stack?
Mammoth greater spirit ability:
Strength of the Beast (Ex) The shaman gains a +2 enhancement bonus to her Strength score. This bonus increases by 2 every 6 shaman levels thereafter (at 14th and 20th levels for her spirit, and at 18th level for her wandering spirit).
Orc bloodline power (through Eldritch Heritage feats):Strength of the Beast (Ex): At 9th level, you gain a +2 inherent bonus to your Strength. This bonus increases to +4 at 13th level, and to +6 at 17th level.
Not that I expect to get that far along. We mess around too much.