You cannot disable emoticons in chat rooms that are hosted on a Microsoft Lync Server 2010, Group Chat server.
To resolve this issue, install the following cumulative update:
2500447 Description of the update for Lync Server 2010, Group Chat Server: April 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
After you apply this update package, you can configure the Lync Server 2010, Group Chat server to disable emoticons in chat rooms, or you can do it by using Group Policy object (GPO).