If Mikrotik routers ARP list contains entry's without corresponding MAC’s (device dos not exists), then The Dude shows fake MAC’s in its section Devices → MAC Mappings.
All non-existing/unknown MACs in Dude -> Devices -> MacMappings menu are marked as "XEROXCORP:00:06:00"

In other TheDude menus, like view in particular device SNMP or RouterOS tabs, ARP list is correct.

Check exmaple in screenshots.