I'm pretty sure, even if you edit the echo mode I describe below, when using !<command>, they will echo to players chat, at the least, as the text you typed.
Try mode 0. If it works, great. If not, use the console ulx commands. (I still find it's autocompletes on clients far superior to chat commands in most cases.)
Either edit your gmod/data/ulx/config.txt, or find where to change modes in XGUI.
(if file doesn't exist, copy first from gmod/addons/ulx/data/ulx/config.txt to gmod/data/ulx, then edit.
Starting at line ~30 of config.txt;
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"
ulx logEchoColors 1 ; Whether or not echoed commands in chat are colored
ulx logEchoColorDefault "151 211 255" ; The default text color (RGB)
ulx logEchoColorConsole "0 0 0" ; The color that Console gets when using actions
ulx logEchoColorSelf "75 0 130" ; The color for yourself in echoes
ulx logEchoColorEveryone "0 128 128" ; The color to use when everyone is targeted in echoes
ulx logEchoColorPlayerAsGroup 1 ; Whether or not to use group colors for players. If false, it uses the color below.
ulx logEchoColorPlayer "255 255 0" ; The color to use for players when ulx logEchoColorPlayerAsGroup is set to 0.
ulx logEchoColorMisc "0 255 0" ; The color for anything else in echoes