I want to do something like "if campaign=xxx" {include footer} in System Workflow Messages
So you need to find out if the campaign id is assigned to a variable available in the message template. 

I can't test right now, but if you enable debugging and add a {debug} if you template you should get a long and fugly table with all the variables available from the message.

then it's the same process as for the contribution page:

{if $campaignID == 1}
{* whatever you need to do on this message *}
{/if}


campaignID to be replaced by the variable available to the template as identified in the debug message.