If someone (not a Paladin) is casting this spell, does it continue to reduce the armor hindrance of Paladin spells (ONLY) being cast?
Or does it reduce the armor hindrance of "that person's profession list" being cast?

Not even sure it would reduce paladin circle for them, unless they had SK 1600's ranks, because the reduction % is based on paladin ranks known.

Sweet is the sound of the pouring rain,
And the stream that falls from the hill to plain.
Better than rain or rippling brook,
Is a mug of beer inside this Took.