Radius authentication is something that I haven't configured or supported, so I can't speak to that much. However, linked below is the manual for firmware version 6.6.3. Page 1001 starts a section for radius commands. It should be of use to you.

https://dell.to/38eaoPn

Hi,

there is nothing described in the CLI guide about that.

Only in the manual is a small part about managing trunkports via radius  

RADIUS Trunk Mode Assignment
Some network administrators may choose to use a default configuration on all
ports in the network and administer bespoke network policies via RADIUS.
Dell EMC switches support configuration of switchport trunk mode on ports
via RADIUS. In an 802.1X Access-Accept message, the Cisco VSA devicetraffic-class=switch indicates that the connected device is capable of
forwarding traffic from multiple stations using tagged and untagged traffic.
When an Access-Accept message is received that contains the VSA devicetraffic-class=switch, the switch operationally sets the port to trunk mode and
utilizes the RADIUS-assigned VLAN to set the operational native VLAN. If
not present, the port PVID is used to set the operational trunk port native
VLAN. Spanning-tree portfast is operationally disabled on the port. Any
trunk mode configuration on the port is respected.
NOTE: MAB and the guest VLAN feature are mutually exclusive on a port. If MAB
is enabled on a port concurrently with guest VLAN, the port will not move to the
authorized state.
360 Authentication, Authorization, and Accounting
Additional hosts may authenticate on a switchport trunk (or general) mode
port configured in authentication host-mode multi-auth and contain a VLAN
assignment. If the Access-Accept contains a VLAN assignment, the VLAN
assignment is honored for the client. Client packets must be tagged with the
assigned VLAN to be forwarded.