You won't find many Socket 370 motherboards with DDR SDRAM support because the Pentium III is unable to take advantage of the additional bandwidth offered by DDR.....an SDR and a DDR P3 system perform virtually the same in most cases.
Certainly, you won't find boards with the requirements you are after (I can't think of any at the moment).
I suggest you look at the ASUS TUSL2. It is based on the SDR i815E chipset, has support for the Tualatin Pentium III, and has a RAID Controller.
If you insist on DDR SDRAM, then have a look at the ASUS CUV266/TUV266, and simply add a PCI RAID Controller.