So...I can't get the Entry Point: Apply Reanimate Spell effect to work. My initial thoughts were that once you have a perk with that entry point, any spell using the Reanimate archetype should apply the chosen spell.
This was not the case for my custom perk and custom reanimate spell.
Custom Reanimate spell: has a Reanimate type effect as the primary effect and a Script type effect
Custom Perk: Only Entry Point is Apply Reanimate Spell -> ReanimateAb
Custom ReanimateAb: Ability that adds 100 health (basically a copy of the ability used by the vanilla Dark Souls perk)

I give myself the perk, give myself the spell, check an NPC's health with the console, kill it with the console, cast Reanimate on it, check its health after it has finished reanimating, health hasn't changed.

So I tried it with the vanilla perk and the vanilla Reanimate Corpse spell. Same result.

Can someone check if this is working for them?

Hmmm...to answer my own question here: It would appear that having 2 perks that use the Apply Reanimate Spell entry point break that entry point. You don't even have to have them both on the player, they just need to exist.

Tested it by: removing the entry point from my perk, adding the perk Dark Souls to the player. Reanimate spells (even my custom one) give the Dark Souls bonus ability.
added the entry point back to my perk, added the perk dark souls to the player. No Reanimate spells give the Dark Souls bonus ability.

using different priority values does nothing.

-Que Insane Laughter-
Turns out it doesn't matter anyway. I had thought abilities added by this entry point would be immune to the spell effect/ability stripping that happens to reanimated actors after/during/before? load screens...I was wrong.

So very, very broken

Hahah. Have to admit I don't entirely follow what the problem is but it's kinda funny to watch you talk to yourself about it.

I haven't played with Reanimate so I poked around some. Why are you looking at the ability? The targeted spell I found doesn't add 100 health, it is simply a Conjuration spell on the targeted actor with checks for a perk and valid target. And we can't change the way the Conjuration behavior functions in the CK.

And.. .ummm... after the laughter. Oh. Hrm. Maybe you were wanting to get around the Conjuration lock-out?

Heh.

Yeah, probably seem kinda crazy right now...I've just been derping around with this reanimate business all weekend and its annoying, to say the least. I kept experimenting with it after I posted the OP and, like a boss, came up with an answer before anyone else posted ;P.

What I'm trying to do:
-Let the player have multiple (4 for the moment) reanimated Thralls (i.e. 999 day long reanimate spells) at once. This works, I have a spell/quest system set up that tracks the number of Thralls and only casts a short duration reanimate once the player has hit the limit.

-Give the player access to the inventory of these Thralls without having to kill them to loot the corpse, provided they are humanoid type actors and can equip stuff they're given. This also works. I can add and remove stuff from them all day and they can re-equip themselves like champs.

This was the main functionality I had intended to create, so now I'm trying to balance it. I had thought that using the perk Entry Point that Dark Souls uses could circumvent one of the most frustrating limitations of the Reanimate archetype detailed in http://www.gamesas.com/topic/1366341-massively-annoying-bug-with-commanded-actors/page__p__20623423__hl__reanimate__fromsearch__1#entry20623423. When Reanimated actors go through certain load screens they are stripped of any spell effects/abilities they are being affected by.

This is a bug present in the vanilla Reanimate system. I think the devs just slapped an extra effect on their spells (the one that turns stuff to ash when it dies) and called it a "feature".

I figured that since the Apply Reanimate Spell entry point seemed to be hard coded into the Reanimate system, abilities added with it would persist on the actor through load screens. They are stripped like any other effects would be.

Edit: To state the conclusions from my first 2 posts more clearly: if I want to use the Apply Reanimate Spell entry point, I would have to modify vanilla stuff (something I'm trying to avoid). This is merely an annoyance as I can accomplish what I need with scripts...Using a perk would have been far easier though, if only it had worked properly.