Well according to the 2.4.19 changelog support for the 20276 controller was added in 2.4.19pre5. The kernel that comes with Red Hat 8.0 is patched to 2.4.19pre10-ac1.
I looked at the source code for the kernel that comes with 8.0 and the PCI ID for the 20276 is listed.
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However, since I don't have one of these controllers I can't say that it actually works. Or if the raid features of the card are supported. More then likely raid support is only via linux software raid. Which you would probably be better off using anyway.
IDE RAID controllers do not perform their RAID functions in hardware. They essentially perform software raid in the controllers bios.