It seems that several people have been having problems getting Dell OMSA 6.2 to work correctly on CentOS 5.4 x86_64. Specifically, the software does not detect any storage controllers, and therefore also doesn't find any disks. eg.
[root@b034 ~]# omreport storage pdisk controller=0 Invalid controller value. Read, controller=0 No controllers found.
After a little investigation, I found the source of the problem.
It turns out that the i386 package of compat-libstdc++-33 is required, although it's not pulled in as a dependency by the srvadmin-whatever RPM.
yum install compat-libstdc++-33.i386 service dataeng restart
Now, the same command works just fine:
[root@b034 ~]# omreport storage pdisk controller=0 List of Physical Disks on Controller PERC 6/i Adapter (Slot 1) Controller PERC 6/i Adapter (Slot 1) ID : 0:0:0 Status : Ok Name : Physical Disk 0:0:0 etc.