Most of the sets I've seen for Serperior are offensive, so yes, Serperior can indeed be used offensively and I'd say it is completely worth it to EV train it in Attack or Special Attack, depending on the kind of moveset you use.
By the way, I'd recommend using a Specially offensive Serperior if you have one with the ability Contrary, which makes all stat changes have the opposite effect. This is because Serperior gets Leaf Storm, which with the ability, would give Serperior a +2 Special Attack boost each time it uses the move. I'm sure your Coil set would work pretty decently too, though.
Hope I helped!