There's far more lethal instruments of bio-warfare than Ebola that ISIS could use.
I'm betting on ignorance of people who eat dead (from Ebola) monkeys found on the streets and then go to witch doctors when they get sick.
Seems to me it is an exquisite suicide weapon. It is sinister, devious, and evokes a high level of terror, which appeals to Jihadists who are always coming up with new ways to conceal destructive devices. Unlike a body bomb, no one can detect this one (approx. 20 day incubation) until it's too late. Also the medical profession relies on followup to identify those who have had contact with a diseased carrier as a means to contain the spread. Fat chance you would get cooperation in this instance. Just think if there was a coordinated attack by a dozen or so in major metropolitan areas in the U.S.