Performance Impact between databases
The same MySQL process will use the same CPU cores to process and move data between the same disk and the same memory, whether your reporting table is in the same MySQL database (schema) or in a different schema. Even if you have a separate MySQL instance on that machine, it will still compete with its sibling for hardware resources. For proper isolation you need a separate server.

A typical scenario includes a master-slave replicated pair, with reporting workload hitting the slave.