Yes, assuming you can get the data OUT of DB2 in a meaningful/useful format. Splunk is not purpose-built for this job (like say the Optim Database Performance tools), but it can be made to do this.
One of the applications I support (NOT SAP) using Splunk has an application-level log of SQL statements issued and the amount of time they take (yes, this is a lot of data - most of our license volume). We have been able to use this to drive many different application performance troubleshooting scenarios involving slow DB2 queries. Note this is an application-level function and not a DB2 facility specifically.
One specific ways you might be able to use Splunk (and the DB Connect app) to help understand DB2 performance is to use the DB2 snapshot tables/views. DB2 provides a very nice facility for accessing some of its internal snapshot state by doing SQL against some administrative views. See http://www-01.ibm.com/support/knowledgecenter/api/content/SSEPGG_9.7.0/com.ibm.db2.luw.admin.mon.doc... . It would not be difficult to have Splunk do a periodic capture of these, index them, and use it to gain insights.
This is a case where I am not aware of any pre-built Splunk app for DB2, so you would have to spend a lot of energy on this yourself. Whether or not that is better or worse than finding/buying a tool specific to database performance is entirely situation dependent.
