If the user takes away the summon's personality they can't resist the summoning because there's nothing to resist with. Orocihmaru with the first hokage and second hokage quickly took their personailties because there could have been a chance the third hokage could have striked some emotional weakpoint given their history with each other.
But on the flip side taking the personailites of the edo tensei's means you have to control the summons yourself meaning you have to know how their abilities work. For example kabuto didn't take full control of Deidara becuase he doesn't understand how his explosive clay works.
Kabuto with itachi and nagato won't be reakless by leaving itachi and nagato free to do what they want. They are among his strongest summons like the haxed kages he summoned like the 2nd stone kage, don't forget that. I think the true question would be does kabuto understand how to use the rinnegan? Kaubto has mentioned he wants to learn about the rinnegan and the so6p so I reakon nagato will be his riskest summon out of the lot. I imagine from orochimaru he would have a good idea how the sharingan works.