Server platforms definitely need UEFI or something very much like it. How else can a server boot from eg. a network card that's not directly supported by the firmware? You need something like UEFI to define a standard for option ROMs, and that standard needs a stable, backward-compatible ABI.

AFAIK, only UEFI and ACPI fulfill that requirement currently (ok, there's Open Firmware, but that's quite esoteric) - eg. Coreboot doesn't really work well in this situation: multiple vendors, different update lifecycles and possibly closed-source binaries.