Aura of decay isnt gaining +levels from Tongue Of The Abberant Seer and rotmind!!
This is a known visual bug. You can still allocate the points.
Im sorry but i cannot, the visual bug happens on wandering spirits and spirit plague but not on aura.
Yea its still not fixed. I got item which gives +1 to poison skills. It gives a skill for Wandering spirits (which does necrotic damage, because I havent used point in it which converts it to poison) but doesnt give a skill point for actual poison skill “Aura of decay” 
That item is +1 to poison spells. Aura of Decay is not a spell.