Nimbostratus
Cirrostratus
It should be possible to increment counters in a stats profile to track the connections. You'd increment the counter in SERVER_CONNECTED and decrement it in SERVER_CLOSED.
However, I'm not sure it's worth trying to track the number of connections to each pool member in an iRule in order to make this data available for monitoring or reporting. It would probably be more efficient and scalable to use a remote host to poll for this type of info through SNMP (assuming it is available via SNMP?). Quite a few people use Cacti for this type of requirement. F5 recently published an implementation guide for using Cacti with BIG-IP:
SOL11167 - Deploying the BIG-IP LTM with the Cacti Open Source Network Monitoring System
https://support.f5.com/kb/en-us/solutions/public/11000/100/sol11167.html
Another option might be to create a read only account and have people check the statistics page for pools.
Aaron