iRule not triggered on target VIP after using the virtual iRule command to direct traffic to it

The problem is in your syslog-pool-select-v4 iRule. Although your switch statement will set the destination to the virtual, your else statement at the bottom will send it to the syslog_pool_Channel_0 pool instead, essentially overriding the earlier "virtual" statement. In your case, you need to make sure that you don't call a "pool" command if you've already called "virtual". There are a couple ways of doing that; the easiest might be to do a "return" after calling your log statement.