Plasma Scoring says that you get an extra die when one of your units uses space cannon. So do you get the extra die when playing the experimental battlestation card? It just says you get space cannon in a system that has one of your space docks, implying that the space dock shoots the cannons but not explicitly saying that it comes from a unit.
The action card says "That space dock uses SPACE CANNON 5 (x3) against ships in the active system."
So it does explicitly say that the shots come from a unit.