Yes, legacy can work with OS 3.0.1 and Radiance 5.3 but you have to follow this workaround to get legacy to work with OpenStudio 3.0.1:
Alternatively, you can install whatever engines you want to use with the new plugin in the C:\Users\[USERNAME]\ladybug_tools folder. The new plugin knows to look for engines there but the legacy plugin will not look there.