Actually, per this guide, the armor scaling (seems there may be a added toughness in general not scaled off the WD) of passive summons does not occur since 2.0.4? No idea how accurate
[Guide] Fetish Psychopaths Build - Forums - Diablo III
"Patch 2.04 Update: Reported change, will update if found to be false.
Difference between Fetish Army and Fetish Sycophants.
Fetish Sycophants no longer have force armor. This means they are more prone to be one shot or melted by regular white enemies such as Morlu Incinerators or Dark Berserkers.
Fetish Army remains the same as before and survive better than FS fetishes.
Dogs and Gargs still have force armor."