Currently buffing a pet with Base AF does NOT provide the pet with any armor/absorb. The pet should receive ~1.8% damage reduction per 10AF.
I tested this by attacking a Necro's pet to get the baseline damage unbuffed, buffed the pet with a 50 Enhance Cleric with Mastery of Arcane 3, and used the level 42 spell Aura of Deflection. This should have resulted in the pet having a 68 value AF buff for ~12.24% damage reduction. Melee damage before and after buffing remained the same.
I tested this by attacking a Necro's pet to get the baseline damage unbuffed, buffed the pet with a 50 Enhance Cleric with Mastery of Arcane 3, and used the level 42 spell Aura of Deflection. This should have resulted in the pet having a 68 value AF buff for ~12.24% damage reduction. Melee damage before and after buffing remained the same.