Its my understanding that the COMPARE procedure only runs in the SAS environment. What that means is when you reference a DB2 table with COMPARE the entire table (or subset if chosen) will be copied into SAS so that the comparison can happen.
I've used COMPARE with multi-million row tables easily without any problems but have not tried > 144m rows. In theory as long as you have the resources it should work OK. I suggest you give COMPARE a go first before trying anything else. Its a great tool that is not used as widely as it could be.