Dimpling is useful to prematurely trip the flow to turbulent so that it stays attached to the shape longer. You gain drag from dimpling, but you lose drag from keeping the flow attached longer, thereby reducing the form drag.
Shapes which are already fairly aerodynamic, and particularly if they are not at low Reynolds numbers, aren't going to benefit from dimpling. On the contrary, it will increase the drag.
Even if one thought dimpling the nosecone of a rocket were a good idea...
Dimpling is just one form of turbulator. What you are doing is attaching a turbulator to the surface of the object in question.
Now a golf ball has no preferred orientation. So to get the turbulator to work well, it has to be pretty much everywhere. Hence the dimpling all around it.
A rocket has a preferred orientation...
Now a turbulator typically trips the flow to turbulent 10-20% downstream of the turbulator, relative to object size. But that's for airfoils on wings.
The flow on a rocket nosecone should intrinsically be fully laminar or nearly so, which provides the lowest drag you are going to get for that portion of the rocket's total surface area. How far flow can remain laminar after that is TBD... Depends on Reynolds number, shape, Mach number, angle of attack, spin, oscillation (unsteady flow), and possibly some more etceteras of decreasing importance.
Generally a boattail is a more appropriate solution for a rocket. Having dimples a little ahead of the boattail may help the flow stay attached around the boattail better, thereby reducing form drag. Whether that is a net win or loss for drag depends on some things...
For one, while the motor is burning, the form drag is lower by quite a bit. That's useful for those trying for high altitude flights. Integral of drag force over time + integral of gravity force over time gives energy lost to gain the altitude.
At low altitude, atmospheric pressure is highest. But the motor is burning so form drag is intrinsically lower. You'll have the cost of the drag induced by the dimples, but will lack the intended benefit. The rocket exhaust plume is filling the hole at the base of the rocket just fine.
Then at higher altitude, the motor cuts off. Now this is a region where dimples or some other technique to keep the flow attached and form a narrower wake could potentially offer some benefits. But atmospheric pressure is already reduced somewhat or a lot, depending on the flight profile. So the benefit on that integral of drag is reduced a little or a lot.
However the cost of the additional skin drag from the dimples was there the whole time.
So for a rocket, assuming performance is the goal, dimpling is unlikely to yeild a benefit and is more likely to yield cost.
And in the transonic to supersonic range, that cost may be quite high.
(I didn't proofread the above unlike usual - I'm out of time. So hopefully I didn't typo anything or leave off anything basic)
Gerald
