You need to throw out this notion of Ivy league when it comes to graduate school. Ivy history depts aren't necessarily the "best" nor the most competitive. The individual departments and programs earn their reputations aside from which college or university they happen to be housed in. Further true for the fields/specialties within these individual departments.
The history departments at Michigan, Chicago, Stanford, Berkeley, etc. may be just as competitive/prestigious as any of the Ivies. And the deptartment prestige is only as important as the strength of the professors in your area of study: US, modern Europe, China, etc.
Short answer: Undergrad publications aren't expected or required for grad admissions, but they will certainly give you a competitive advantage over comparable applicants without.