I remember reading that Savagery damage multiplier boosted weapon pool procs damage.
Is this true for other procs like devotion or item procs?
Yes, it boosts devotion and item procs too 
I don’t think it does. The fact that it boosts WPS lies in the inherent nature of how WPS work: if you use Fire Strike (120% weapon damage at rank 12), it boosts WPS damage by 20% as well. The difference to this with savagery and the other charge-based basic attack replacers is that it adds another multiplier, but that multiplier only affects savagery damage. It woudl work like this:
Rank 16 Savagery at maximum charges has a 115% damage multiplier for Savagery. The base damage on the skill at that rank is:
150% weapon damage
22 Lightning damage
26 bleed damage over 3 seconds.
Thus, the 115% multiplier due to the charge system changes this to:
1,15x150%=172% weapon damage
1,15x22=25,3 Lightning damage
1,15x26=29,9 bleed damage
If an attack with Savagery were to proc a WPS, that WPS’ damage would be increased to 172% of it’s base, as that is what weapon damage Savagery deals at that moment. Not because of Savagery’s charge muliplier, that only applies to the skill itself. Thus, no increase for devotions and item procs as those apply independently of whether you use savagery or any other skill they can be bound to.
If I am wrong on this, someone more knowledgeable feel free to correct me but this is how I am fairly certain it works.
Idk, I tested it with a savagery-using lightning character, and while the savagery charges are active, all procs(i.e. lightning nova from ultos weapon or arcane bomb devotion skill, etc.) show significantly higher dmg numbers.
And there’s another thread about savagery mechanics, and iirc it was stated that the +%lightning and bleeding from savagery are a general buff to the character as long as charges are active…
Yep, Savagery charges definitely boost non-Savagery attacks too.
As far as I under stand it, the lighting and bleed “buffs” get applied to all skills/proc/devotions. Only the skills/proc/devotions with % WD (and only this portion of said skill/proc/devotion) will scale with the charges of savagery. The tool tip for skills will only who what 100% (converted to your %WD your skill has) WD is and not show the scaling with the charges. Although your actual damage with chance.