I'm a current student, let me clarify. I have guaranteed funding. I expect most other PhD students in the program have guaranteed funding. Even some of the Master's students have funding. I obviously don't know about every student's funding status, so there may a small number of PhD students who do not have it. However, UNC biostatistics absolutely does guarantee funding explicitly. They will send you a letter specifying your exact stipend and the number of years they will guarantee it. As I recall, the funding letter came shortly before the visit day. If you don't get a letter specifying your funding, you don't have guaranteed funding.
As to the tuition waiver, it's not something to worry about. Your first year funding covers out of state tuition. After the first year, you will have lived in North Carolina long enough to establish residency and therefore will be eligible for in state tuition. Getting in state residency requires submitting a few forms to the state. You be reminded many times by the department to do this.
