I think the photo rosters would be a great way to promote class interaction in my class by speeding up the process by which students recognize and learn each other's names. May I share the roster with them?

No, this would be a FERPA violation, unless you obtain the specific written consent of each student in advance. Class rosters contain personally indentifiable information, e.g., photo and ID number, which is protected from disclosure to third parties, even classmates, by FERPA. Such rosters are intended for instructor use only.