The average weight of a kernel of Varget is ~1.4 mg, or approximately 0.022 gr. For H4895, the values are 1.1 mg, or about 0.017 gr. Each powder kernel's average weight will be different, in some cases by a lot. The theoretical effect of a single kernel on velocity is equal to:
(average weight of a kernel/ total charge weight) x average velocity
As expected from the above equation, the effect will vary depending on the average weight of a kernel of the specific powder used, the charge weight, and the average velocity achieved in that specific load.
The question originally posed by the OP was, "Is your aiming accuracy @1000 yd comparable to one kernel?". The specific answer to that should be "No". Anyone claiming to be able to hold a finer increment at 1000 yd than the vertical produced by about a 1-2 fps velocity variance (or less) is pulling your leg, or simply trying to BS you. The amount to which that amount of powder will affect velocity falls well under the SD for even very good loads, and is approaching or below the limit of detection for most chronographs. Nor is it ever possible to state with any certainty that someone lost a match because they didn't weight their powder to the same precision that someone else did. That type of information is always going to be anecdotal at best. No one will ever know how they might have done if they did something different with an effect as small as one kernel of powder. I'm absolutely certain that there are those that absolutely believe they can, but they're fooling themselves.
Winning or losing in a match by ridiculously small measurements is never proof of what actually caused the group to be infinitesimally larger or smaller. It might have been charge weight variance, it might have been neck tension variance, it might have been a difference in primer brisance, it might have been a little puff of breeze the shooter didn't see, it might have been a trigger error by the shooter. There are dozens of potential reasons why a group might be ever so slightly larger or smaller, and when the differences are extremely small, you'll never really know the exact underlying cause, even if you choose to believe you can, because you can never know what you would have shot if something were different.
However (and this is really the most important aspect of the OPs question IMO), why would you NOT weigh powder to the highest level of precision you possibly can, time and equipment allowing? If you weigh powder to +/- half a kernel (I do), you will never, ever, ever have to worry about it in a match. I can never prove I won a match because I weigh powder to this level of precision, it might have been some other reason. I can never prove I lost a match because I didn't weigh powder to this level of precision, it might have been some other reason. What I CAN do is to make absolutely certain that wherever possible, I hold the tolerances for a specific load well below what I can actually shoot. Weighing powder is one place where I can do this with minimal time and effort. It costs some $$$ to buy a quality force restoration balance, but they last almost forever, if properly cared for, so IMO they are a good investment for LR reloading/shooting. At that point, the precision to which you weigh powder simply ceases to be a consideration, allowing you to worry about other things that you may not be able to control as well as powder weight variance.
A good friend of mine and member here at AS (Steve Blair) made a statement about reloading that has always stuck with me. You can choose to do some potentially painful step (in terms of time and $$$) in the reloading process, or you can choose not to do it. However, you can always be pretty certain that at least some of your competitors WILL be doing it. So even if any advantage of that particular step is small, or even possibly un-measurable, you still have to make the decision to incorporate it or not into your reloading scheme based on the knowledge that other people will be doing it.