Ok, be more clear. ULX has two types of notification (more actually, but, for this conversation, 2 related to chat commands)
1) You want to see someone saying "!slap bob"?
Fred: !slap bob
OR
2) You want to see the notification that someone slapped bob?
Fred says "!slap bob" and after that
{Someone} slapped bob 1 time
There are several ways to change or hide option 2, but, if you're actually not seeing someone say it as in option 1, you have a conflicting addon that's watching for "!" commands and preventing the echo of the chat, even though ULX might still work.
We don't hide chat by default. Though our code has ways to edit and prevent it, I just checked, and our github slap doesn't do that.