MAssive blow and all the physical abilities in shaman, justicar, and druid souls are exactly that, physical abilities. Any benefits which apply only to spells do not apply to them. Any abilities which increase spell power or spell crit directly (not spell crit chance for example) benefit melee abilities because your passive converts spell crit to physical crit and spell power to physical power. I believe there is a minor exception to this and that is when your abilities deal elemental damage. So for example the lightning damage from lightning hammer and jolt damage may be affected by moves that increase spell damage, but I'm unsure of this.
Inner focus will not affect massive blow.
BUT the game suggests you pick Druid and Justicar when making a Shaman, if thats the case, does Faith in Action stack? If not, and if your focusing more on just doing raw damage, I can't see why you'd go Justicar, when Shamans seem to focus so much on Criting, and they can get the buffs from the Inquisitor tree.
Faith in action does not stack, as it would be tremendously overpowered if it did. first you should know that in game suggestions are often merely what developers guessed people should do and often for thematic reasons (shamans melee, justicars melee, more melee = more good right?) Don't trust in game tips. Edited, May 31st 2011 7:09pm by Allegory