Hi,
Generally, multi-pathing policy should be set as per Storage vendor guidelines/recommendations. If the vendor suggests a particular policy, configure it in your VMware environment accordingly. The same policy applies to every LUN, including RDM.
I have seen Round Robin configured across environments. Below are some good links which will provide more details.
Change the Path Selection Policy: https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.storage.doc/GUID-AE95818C-0782-429B-9526-DF12673A63C7.html
VCP6-DCV Objective 3.3 – Configure vSphere Storage Multi-pathing and Failover: https://www.vladan.fr/vcp6-dcv-objective-3-3-configure-vsphere-storage-multi-pathing-and-failover/
Let me know if you have more queries on this.