From VMware website product overview:
vRealize Operations Manager:
vRealize Operations lets you automate IT operations management, manage performance and gain visibility across physical and virtual infrastructure.
vRealize Log Insight:
vRealize Log Insight delivers heterogeneous and highly scalable log management with intuitive, actionable dashboards, sophisticated analytics and broad third party extensibility.
So, while vROPs collect primarily structure data, like performance metrics directly from solutions like vSphere, the vRLI collects unstructured data, like log messages mainly via Syslog.