Vex is treated like a fusion rifle. Reload bonuses apply to the weapon in the primary or secondary slot. Special weapons loader does not benefit NLB or UR either. Special weapons loader bonus only loads weapons in the secondary slot. It's the way they coded the perk to classify weapons. They should probably make the perk apply to each individual special weapons class the way ammo bonuses do, as opposed to tying it to whatever ypu have as a secondary. It is funny that they forgot about it tho. It's likely how the OG Vex had such absurd damage values. What's most likely is that they wanted to nerf the Vex along with the ARs, but couldn't come up with a way to do it while still making the deadline of their promise for end of February. So they let it take the blanket Fusion nerf instesd of allowing it to be default best gun in the game again by being unchecked.