What do you mean by "archive logs backup"?
When you set LOGARCHMETH1 to "userexit", you must place a userexit routine in the appropriate DB2 directory for this to work properly.
I assume you are trying to have your logs archived to your backup software. To do this, the backup software must supply you with the userexit routine to do this.
Are there any messages in the db2diag.log file about archiving logs (whether they are successful or not)?
Andy