I'm writing the following post to provide a detailed explanation on the Minion Ele Dmg situation so that I can link to this post for users who want more detail.

In the original game, Skeleton Mastery does not scale the elemental damage of the Skeletal Magi. The +Damage% listed on it strictly applies to the physical damage of the melee skeletons.

So that means that the only way in which the Skeletal Magi gain damage is through flat damage per level. To improve this in PoD, I had previously given them some +Elemental Damage%, the same found on Rainbow Facets, Sorc Masteries and unique items like Griffon's Eye (+10-15% To Lightning Skill Damage). This way, the +Damage% from the mastery (now called Summon Mastery) would benefit both Phys and Ele.

Vanilla Revives also gained +Damage% from Skeleton Mastery (hidden bonus) but again this only affected physical damage of revives and therefore wouldn't help monsters that deal elemental damage. So I gave revives the same treatment, granting them the +Elemental Damage% stats to scale their damage.

Unfortunately I realized that while the tooltip was listing the correct & expected values, the actual damage being dealt was lower. It is clear now with more thorough testing that the mastery was not in fact increasing ele dmg whatsoever. I think this was not made immediately apparent at the time of implementation because it was done alongside a large buff to the flat elemental damage per level so they did feel much better than vanilla. The synergy provided from Bone Offering also wasnt working for the same reason. So why doesn't it work? Because for whatever reason this stat is not included in damage calculations for when a monster deals damage. Strange since most player stats also work on minions like physical damage, movement speed and resistances.

That's not all the issues though. I couldn't add elemental damage to Bone Offering because it would affect players too and increase their damage too much so Bone Offering was less useful to ele. And now I know that even if it had added elemental damage, it wouldn't have affected them anyway. As if all of this wasn't painful enough; I couldn't add a minion-only elemental damage stat to Bone Offering because if the buff granted some kind of minion specific stat that then increased the dmg on Raise Skeletal Magi skill then this would not immediately apply because passive buffs are snapshotted onto the minion at the time of summoning. This means even if I had elemental damage working, a minion-only variant wouldn't be possible unless you resummoned them while the buff was active which would then snapshot the buff on them until they died.

TLDR; Diablo 2 'softmodding' is a pain in the ass.

It's not all bad news though. I found a way to provide minions with real-time increases to some stats in order to fix the snapshotting issue. And I've also found a way to apply the damage% increases to the skeletal magi from both passive and active buffs. In the future I also want to apply this new dynamic stat system to all other minions in order to allow for greater design space.

So in the end what does that all mean for you guys: The elemental skeles will now actually deal the damage listed on the tooltip which results in a nice buff. It also means that Revives do not currently gain elemental dmg at all because I haven't found a solution for them yet. 

I'll keep working on this and improving it. Sorry for the overly technical wall of text.