Liam,
You are quite correct. The essential thing to note is Redhat support for whichever RAID chip the motherboard is using. The next important thing to note is the kernel version supported by drivers for the RAID chipsets.
Most vendors will only provide precompiled drivers for kernel 2.2.16 and 2.4.x for Redhat 7.0 and Redhat 7.1. This means they "should" work with ESSG 4.1.2 (which uses kernel 2.2.16) and I have successfully used Highpoint based cards (like the Adaptec 1200A) with the drivers from the Highpoint web site.
However, they will NOT work with SME 5 due the the kernel version in use, 2.2.19 and unless you can get the source files to recompile for the 2.2.19 kernel, I'm afraid, you're probably out of luck (as I was when pursuing support for Highpoint based cards under SME 5).
Hope this helps.
Kelvin