The bubonic plague did work for the mongols. Killing 1/3 of the population of europe. If ISIS use ebola as a weapon I don't think this will not work for them. Ebola just infected an american nurse in dallas without the terrorist help how much more if the terrorists is added to the equation.
Probably trying to spread ebola wouldn't be a great success. How these infected terrorist can inject their bodily fluids into many people without being noticed? Sneezing and coughing on crowded buses or trains? Yes that could do some harm but I think they would be more effective with a few dozens of traditional hand grenades.
It seems to be spreading without anyone trying, are you thinking there is very little chance that it could be worse than it is now if the virus conscripts human wickedness in its war on humanity?
Sneezing and coughing on crowded buses/trains/events. Yes, they could do that first.
Historically, also by blowing one's self up in crowded places so that it can be time-synchronized in multiple locations for maximal terror effect.
The few dozen grenades would be optional, or even improvised mines in the places where people would naturally run from the chaos.
This could put infected people in hospitals for stays long enough so where symptoms would ultimately manifest in the hospitals.
The win for the terrorist here, is the imposition of martial law by your own state.