Site-based Invoicing and Transparency Enhancement Act or the SITE Act This bill modifies the payment methodology for services that are furnished at off-campus outpatient departments of hospitals under Medicare. It also establishes a nurse training program through hospitals. Under current law, off-campus outpatient departments of hospitals that began billing prior to November 2, 2015, or that were under construction as of that date, are exempt from certain site-neutral payment requirements under Medicare. The bill ends this exemption. It also (1) reduces payments for services furnished at off-campus outpatient emergency departments that are six or fewer miles from a hospital, and (2) requires off-campus outpatient departments of hospitals to have unique health identifiers. Additionally, the bill provides for funding of regional nurse education hubs. The Centers for Medicare & Medicaid Services may select one hospital in each referral region to operate as a hub for training, in coordination with nursing schools, Medicare and Medicaid providers, and other training partners. The bill provides for up to 20,000 nursing student positions in the program by 2030.