Not exactly. You still have to update back to the firmware you were previously on, and even if you do get that, I'm pretty sure you can brick by running your compiled OTP through the hb menu (don't quote me on that though).
All having a 2.1 emunand will do is confirm that the emunand downgrade worked, it doesn't confirm that the dump itself isn't faulty (just make a few dumps and check it's checksums), and downgrading and updating using anything, even Decrypt9, will always have a chance of a brick no matter what. Nothing touching the NAND can be 100% brick proof afaik.