You’re absolutely right, you can’t monitor that I/O for DB2 tables – and this is because the DB2 subsystem is doing all the I/O for you.
Most people aren’t as much interested in the actual I/O for DB2 calls, unless you’re a DB2 DBA. They’re more interested in the DB2 calls, and how long they take. To monitor these, you’ll be interested in some of the DB2 monitoring software out there. You can also get this information from SMF records produced by DB2 – your DB2 DBA is the one to talk to here.
Hope this helps.