Will DB's be able to get the +12 helms?

There's no reason to, so unless Nexon makes a specific effort to keep Bladers out of the PQ for an unknown reason, they should be able to do it just fine.

The way they phrased it, it sounds like they "forgot", "don't intend" or "don't know how" to make changes to adapt Dual Blade's jobID to CWKPQ's whitelist. If the jobID of Dual Blade is indeed 4xx, they probably won't need to do anything for this to happen. I would strongly doubt that Nexon would put effort to change that.