No it isn't, here's the answer:
Originally Posted by goodie
is it possible to flash to official WM6 using SSPL?
The "official" WM6 rom NBH file has the OS part tagged as 0x401 (256Mb NAND) instead of 0x400 (128Mb NAND). Only the new SPL-3.03 included in this "official" upgrade is able to understand 0x401, so SSPL, HardSPL or CrashProof SPL or whatever that's not based on this SPL-3.03 (or newer) will not be able to understand the NBH header type 0x401 and will stop at OS flashing.
The solution is simple:
Unpack the NBH and repack it tagging OS as 0x400, then flash it using SSPL, or whatever hacked SPL choice we have.
Caution: reading THE WIKI may be hazardous to your health!