Not a good idea. It can end up spinning inside the hole (because it's too perfect a circle, nothing to "grab" the dirt), once the wind catches the dish. It's much better to just dig your hole a bit crudely with a post hole digger, and bell out the bottom, and place a bags worth of pea gravel on the bottom for ground water drainage. I also like to slightly notch one side a bit.
If you do it my way, once you shovel in the cement it catches in the nooks and crannies and helps to hold things against the dirt. Don't forget to also drill a hole through the bottom of the pole about 1 foot up, and shove a piece of rebar, or a large long bolt through it. That's to keep the pole from possibly getting twisted inside the cement, when wind catches the dish.
A 50 mph wind can create upwards of 500lbs of force against a dish...
It always amazes me the lengths some guys will go through when installing a pole. I have been buying poles at the scrap yard for $15 or $20 (depending on who is working there when I go there and how much the pipe weighs) and typically these have a pretty good layer of surface rust which I just paint with Rust Reformer. I do not use pea gravel, I do not bell the bottom of the hole, I do not use 20 bags of concrete or anything like that. I whack the end of the pipe that's going in the ground with a sledge hammer a few times to slightly flatten it, then dig the hole with a post hole digger, then drop the pole in and center it in the hole (tamping it a couple times so the bottom goes into the sand a little), then fill the hole with concrete* (typically between 3 to 5 bags depending on how many roots I hit that had to be cut out or how much extra sand fell into the hole that had to be removed), then plumb the pole using a level on several sides, then tamp the concrete to get some of the air bubbles out, then check the plumb once more, then smooth the surface, then check the plumb once more to make sure it is absolutely vertical and then I leave it alone until the concrete dries. Whether because of the pitting on the pipe because of the rust or because I flattened it a little with a sledge hammer, I have never had a pole turn in the concrete on me, nor have I had the concrete turn in the ground.
Now maybe there are places where you have to do more, for example if you get hurricane force winds I'd probably want to do a little more to make sure it doesn't turn. We occasionally get straight line winds that can produce hurricane force bursts but only for a few seconds at a time, and those are very rare. Also I have hit plenty of roots when digging such holes, and they are a pain in the butt to try and cut out sometimes, but never rock - bedrock is probably a couple hundred feet down so no danger of hitting that. If the bottom of the pole hole were hitting solid rock, then I could definitely see where enlarging the bottom of the hole and using some sand or pea gravel for drainage might be necessary. One thing to keep in mind is that drainage really shouldn't be all that necessary anyway; the dish mount should cover the top of the pipe and at the bottom it will press into the sand or gravel. Now if you have that nasty clay that turns hard as a rock after it's been exposed to air, then that's probably where the pea gravel would be especially useful for drainage. But if the bottom of the pole is pressing into sand or gravel in the ground then it should be okay because you're mostly concerned with condensation moisture, and unless you have made your concrete mix far too wet it shouldn't creep under the bottom of the pole anyway, even if you forget to tamp the pole into the sand before shoveling in the concrete.
I suppose if you are on a mountaintop that is mostly solid rock and your frequently get high winds and occasional hurricanes or cyclones you have to do a lot more to keep your pole from moving and to provide drainage, but there are many parts of the country where doing any more than what I do really isn't necessary, other than maybe adding pea gravel or sand in the hole if you hit solid rock or clay. What's more than adequate and may even be ridiculous overkill in one area of the country is probably hardly enough in another.
* Actually before filling the hole with concrete I always run a piece of cheap black irrigation pipe up the pole a ways and down into the trench where my wire will go and tape it to the pole with duct tape, so that the wires can go through the concrete so they aren't as susceptible to damage by a lawn mower or weed whacker. If your ground wire is going to head off in a different direction you may want to put in a separate pipe for that. Typically i run the irrigation pipe all the way from the pole back to the house as it helps prevent damage to the wires from future digging, but not everyone may want to do that. Electrical conduit will also work but tends to be far more expensive, and it's not required for low voltage wiring, but it does look more "professional".
I have revised my post accordingly.
