In the RResqueCommand class the logging location is hard coded. You could change it so it points to /dev/null
In the Resque_Log class under the /lib directory (origing resque-php files) you could change the strictness to make the logging less extensive. When you try this, please make sure that when starting the the yiic rresque command that you should include the --verbose=0 flag to not log everything.
You have two options: