We use Dell OpenManage on Centos 4.5. First you have to trick the OpenManage software (and installer) into thinking you have RHEL. For v4 you add "Nahant" to the end of line of text in
/etc/redhat-release.
Nahant is the code name for RHEL4 and Dell software looks for it to know what type of system you are running.
FWIW the yum repo dell setup doesn't need you to to do that.
Patrick