Configuring Oracle monitor in Performance Center with 3 controllers?

I have configured Oracle 10g client SQL plus from both Controller and Utility server (tnsnames.ora is ok). There are 3 controllers for our PC 8.1 FP2 set up but I have installed Oracle client only on one of the Controller and the Utility server. Now, when adding the oracle monitor through PC user site, I am getting the error below:
"Could not login to database server. ORA-12514: TNS:listener does not currently know of service requested in connect descriptor". I am not sure if I need to install Oracle client on all 3 controllers or need to configure something on the PC admin site so that I can configure Oracle monitor profile for a particular controller?? Pls suggest..