I always thought this is a bit of an odd FAQ, or even wrong with respect to the original intention, but it really can be read either way.
For me, occasions when a
hit is negated should not get disrupt BMs. So, holofields, which in my mind *should* work by making you miss when you thought you hit. In all other occasions you should get the BMs because of the disrupting effect on the formation of the weapon detonating (or whatever) in the middle of it. BMs affect formations, not individual units. You could say then that void shields, gaunts and grots should therefore still get BMs. The fact that those have no saves is nothing to do with the weapon after all.
Of course it's not an exact science (eg a miss could arguably still disrupt a formation), and it's pretty academic anyway - I don't play it "my" way because it's not the accepted interpretation. Its just the way I wish it worked

In particular, the wording of the void shield rule uses language like "stops a hit" I seem to recall.
However I am not convinced about the FAQ as it pertains to grots. The grot rule is specifically about what happens when a grot is killed because it is about the effects on morale. And that is what the rule says too. The BMs for disrupt have got nothing to do with kills, so whether the unit dies or not is irrelevant. I think it all depends on whether you think Disrupt should be interpreted as:
1. "if a unit dies add a BM for dying, and if it is hit but survives add a BM for disrupt"
Or
2. "if a unit is hit, add a BM for disrupt, but don't add another if it dies"
The latter just seems more logical to me, and you also don't have to come up with some convoluted explanation why you get a BM for surviving but not for dying. But if it was clearly supposed to work this way, BMs for disrupt and kills would be additive.