Few things drive HR executives nuts more than dealing with intermittent FMLA leave. When faced with this situation, bear these facts in mind:

Employees must comply with reasonable call-in procedures and no-call/no-show policies affected by intermittent leave.
Employers are allowed to get recertification under appropriate circumstances. They can also put employees in an accommodated position that might reduce the need for the intermittent leave.

HR That Works has an excellent series of podcasts produced by the Franczek firm discussing FMLA leave.