pg. 54 of Pathfinder Chronicles: Classic Horrors Revisited has additional varients and information of combining varient types.
And if you look at the last paragraph on 251 of Pathfinder: Bestiary 1 under Variant Skeletons "Except as noted, these variations
can be stacked with one another—it’s possible to have a
bloody burning skeletal champion."
In the Bestiary 1, I see no mention on combining zombie variants but the Classic Horrors Revisited does include combining multiple varients for skeletons and zombies, not all variant types can be combined though.
For anyone using Skeletal Champions or Zombie Lords in their games, Classic Horrors Revisited does include variants for them as well.