My apologies. I now understand what you are asking.
You want a player to have a "Ignore this player" command.
No, ULX does not have that ability, but as stated by Roastchicken, is likely already in Gmod (sorry, I don't know where)
Roastchicken has already answered your question. See his referenced link for how can_target works.
Unfortunately, the default Gmod mute command would not prevent a player from doing what you wish it not to do, mute admins.