No, any HLU will do, but using HLU 0 is cosmeticaly better, since normally you'd start counting with 0 and not with 1. Furthermore: if you're not using HLU 0 at all, you will be seeing LUNz..... A sort of ghost LUN that represents the Clariion. If you simply put the boot LUN at HLU 0 there will be no LUNz.
6GB as boot LUN for Netware ? Really ? I've been out the Novell scene far too long. I loved that platform.