This study focuses on immune checkpoint inhibitor-naive adults with inoperable metastatic uveal melanoma (a type of aggressive eye cancer that has not been treated with immune checkpoint inhibitor therapies). The purpose of the study is to evaluate the effectiveness and safety of an investigational drug called RP2 in combination with nivolumab, versus ipilimumab in combination with nivolumab. Nivolumab and ipilimumab are drugs that are approved by the U.S. Food and Drug Administration (FDA) to treat several types of cancers, but the combination of nivolumab and RP2 is considered experimental. Nivolumab, ipilimumab, and RP2 are part of a class of drugs often referred to as immunotherapy. RP2 is a herpes simplex virus that has been changed in the laboratory to grow and destroy cancer cells and activate the immune system to attack cancer cells. Study procedures include a screening period (medical history, tumor biopsy, blood, urine and saliva collection, physical exam, MRI/CT scan, ECG); treatment period in which participants will be assigned to receive either nivolumab and RP2 (experimental treatment) or nivolumab and ipilimumab; and follow-up.