If you are using log statements and they are not showing up in your /var/log/ltm file, then something is wrong with your configuration. Try putting this in your iRule
...
when HTTP_REQUEST {
log local0. "HTTP Request for URI: [HTTP::uri]"
...
}
For every request you should see this line in the log file. Make sure also that you put the "local0." part in the log statement or the log messages can be batched up and not stored directly (maybe that's your issue).
If you issue a HTTP request through your virtual and you do not see the "HTTP Request for URI:..." in your logs, then you either don't have a HTTP profile associated with your virtual or the iRule is not set as a resource for that virtual. If both of those are true, then I'm somewhat baffled. Let me know how this progresses.
-Joe