Certainly, there is a hierarchy of risk. Travelers from countries with Ebola outbreaks present more risk than others. Travelers from those countries who have cared for Ebola patients even while using protective equipment present greater risk.
And the greatest risk comes from those who have been in direct contact with Ebola patients without proper protection. The Centers for Disease Control and Prevention recognized this spectrum in its new guidelines for monitoring those with potential exposure.
But the current state of quarantine law presents a twofold problem. The first is that questions of quarantine have traditionally been in the realm of state and local power. In the absence of federal legislation, the CDC can only make helpful suggestions, not enforce rules.