Nathan Horton is symptom free after his concussion, does it change how the hit should be interpreted...?

No. The hit was vicious and clearly out of bounds. Besides that, being symptom free when you're not exerting yourself is completely different than being symptom free when you are working out and on the ice. Just ask Crosby. He felt fine for more than a month before the symptoms came back. The suspension was well deserved and appropriate.