I only had an issue with one kit not running at XMP from, lots and lots of kits, and ironically it was a 3200MHz rated kit that wouldn't hit 3200MHz, or even 3000MHz, even with 1.4v. Have you had many faulty in the build you've been doing?
Couldn't find thread where the guy had asked OCuk and they didn't recommend it..saw this below...guessing that why Ocuk don't recommend as they must get higher returns than other sticks..just a google brings up a bit
https://forums.overclockers.co.uk/threads/xmp-issues.18945439/#post-35358258