I don't believe there is any chance of data loss when using raw devices due to asyncronous I/O. Your reasons for using raw devices shouldn't be based on worries over data loss, rather, the raw devices will give you some performance gain. In a very write intensive environment, raw devices should buy you some performance gains. I have an issue with whether there is a performance gain when using a disk array with a large cache(ex. XP256 or EMC), but I have never found anyone at HP or EMC that would give me a definitive answer. I like to take a look at the bigger picture and look at the extra costs of administration in regards to database management (it's easy to overlook the fact that a raw device is being used). Turning on autoextend on a datafile when using a cooked filesystem can sure save you some headaches.
As for the parameters to use with the raw device, the only issue should be with the size of the data "chunk" at the disk level. For example, the XP deals with data in 512K chunks, therefore DB_BLOCK_SIZE * DB_MULTIBLOCK_READ_COUNT < 512K and DB_BLOCK_SIZE * HASH_MULTIBLOCK_IO_COUNT < 512K.
This was first published in June 2001