RAW is a bin blob if I'm not mistaken (my oracle docs are on the oracle box which isn't booted up now). I never ran into Sys_GUID before, but after some googling, it seems to return RAW(16), which is perfectly usable for a guid, I never knew that! RAW is a type you won't run into that much.
Though as with NEWID() (the sqlserver equivalent): these functions aren't supported by LLBLGen Pro, as the value they generate isn't easily read back. So you set the field of the entity in .NET code to a new GUID value, (in your case at the moment you have to grab the bytearray of the guid) then save the entity.
Though a warning is in order: RAW is threated by Oracle as VARCHAR2, though with binary values. I read several threads where seasoned Oracle DBA's warn for this and suggest to avoid RAW. I can only agree. Consider a CHAR(32) field instead.