It's in the Bestiary, under Skeletons and Zombies respectively. There is no mention of templates or variants under the Animate Dead spell in the Core Rulebook either.
That's pretty much a GM decision. I would allow a template which didn't increase CR, if it matched the style of the character's magic. But templates that increase CR I would reserve for Create Undead, substituting them for an equivalent CR undead type.
Like I said before neither the Animate Dead Spell or the Undeath Word of Power say anything about variants. The only place it tells you HOW to make variants is in the Bestiary!
Whether they can or cannot is never explicitly stated (or if it is then I missed it) and seems to down to DM fiat (as is the case with several of the WoP), general consensus seems to say that you can, but if you're looking for an official answer then there isn't one!
Ok, thanks. I'll talk to my GM.