I SSH into my esxi 6.5 box and type dcui ... nothing happens
Over in vCenter it says it is running ....
Try a different SSH client.
I tried two different SSH clients on the same ESXi 6.5 server to have dcui access over SSH.
Ubuntu Desktop 16.04 Remmina Remote Desktop Viewer - OK
CentOS 7 Remote Desktop Viewer - nothing happens
Sorry I don't have a list of SSH clients that works.