Siddharth,
I strongly recommend the DataPower add on that Haruhiko Davis mentioned previously. However, if that is not feasible for some reason (and depending on what DataPower metrics you want to monitor), it is possible to write scripts to pull the metrics from the DataPower devices using SNMP polling to an external server and then use EPAgent to report those metrics up to Introscope. We used this method successfully for several years before CA developed the DataPower add on.
That having been said, I would be remiss if I did not mention that developing the requisite scripts is very manpower intensive and the scripts often need to be modified/updated following a firmware upgrade. The CA add on provides a plethora of very useful metrics with a minimum of customization/configuration required.