The ArcGIS Server 10 system requirements page says that it supports Red Hat Enterprise Linux (RHEL) AS/ES 4 and RHEL 5. I have RHEL WS 4, RHEL WS 6, and RHEL Desktop 5. I am not sure if any of these version works well with ArcGIS Server 10 without any problem.
Future Proof yourself
ArcGIS 10.1 (including Server)
ArcGIS Server 10.1 will no longer support SUSE Linux Enterprise Server 10 and Red Hat Enterprise Linux AS/ES 4. However, we will support SUSE Linux Enterprise Server 11 and Red Hat Enterprise Linux Server 5.
Offical Source: "Considerations for ArcGIS Server developers: A look toward 10.1"
you can check out here.
i hope it helps you..