I have weapon master training unlocked and new character (necromancer) and I got a greatsword and was using it so I already know they should be able to do it.
Now at 65, I tried to equip the Knight's Ogre Longsword onto it and it just does not wanna allow it. I took off the greatsword I had equipped to it before the latest patch and went to try to reequip that and also could not.