Estlor
Explorer
Both classes has to grant Scale armor for you to get Scale armor. If just one class does, you don't get it.
This is a special case. Battle Cleric Lore, the class feature is what grants you proficiency with scale armor. This is separate from the cleric class's armor proficiency. So a hybrid cleric that picks up Battle Cleric Lore gets the entire class feature - including scale armor proficiency.
However, I'd argue this is a case of RAW versus RAI; there was a similar trick with the Battlefront Leader class feature of the warlords that would let hybrids pick up scale and heavy shield for the cost of 1 feat - even if the other half of the hybrid was wizard, for example - and they went back and updated the feat to require chainmail proficiency. One can (safely) assume if it weren't for DDN, a similar patch would probably happen to Battle Cleric Lore.