Though we made several echo modes, I don't believe we made one to totally hide it from one group but not another.
Closest you could get is mode 1, anonymous.
ulx logEcho 1 ; Echo mode
; Echo modes:
; 0 - OFF No output to any players when an admin command is used
; 1 - ANONYMOUS Output to players without access to see who used the command (admins by default) similar to "(Someone) slapped Bob with 0 damage"
; 2 - FULL Output to players similar to "Foo slapped Bob with 0 damage"
I _might_ be wrong in my understanding of our own mode though.
It's _possible_ mode 0 could be seen by admins, but not players.