Beneficial grubs are often present in compost -- I always find little white ones in mine and let them be. I don't know what yours are, but if they are pests along with the fire ants, you'd better add lots of green and brown stuff to the heap you already have, mix it up (from a distance with those fire ants) and let it heat up again. The fire ants will leave under those conditions, and I'd think the grubs would leave as well.

Don't sprinkle fire ant killer around your compost heap in hopes of killing them. It probably would, but they take the poison back to the nest, and if it's in compost, you're going to have poison in the compost after they die. Better to drive them out somehow, and then what you do if they take up residence in a place away from your garden is your business! (I put out poisoned bait for them on the lawn myself, since there's no other certain way to kill them without killing beneficial insects, too.)

I wouldn't use the orange oil on the compost heap either. Compost is usually home to large numbers of earthworms, and you'd kill them, too.

What I've done is spray a mixture of orange oil and water in a "C" shape around any area that I want to drive them out of. Actually you can make any shape with an opening in it. I spray only enough to moisten the surface, not enough to penetrate below the surface -- I figure the earthworms are able to sense small amounts of it and avoid its presence on the soil surface. I leave the opening pointed in the direction I want them to go. The fire ants will avoid the strip with the orange oil and exit through the orange oil-free area and I can get 'em later. It's worked for me when boiling water or flooding them with hose-water doesn't budge them.

Usually just turning the pile will chase ants away. Fire ants hate sugar if that gives you any clues as to what to do.

The grubs you see finished eating last year some time. The only thing left is for them to become beetles or whatever they are. Using the compost should be fine.

You could use a liquid bait such as Terro but not if the goal is to keep ALL insecticides out. But it would stay mainly enclosed in their bodies. So I'm not sure if that fits with your plan,as far as fire ants hating sugar--that's a new one on me. Not sure if that is correct....I see fire ants ALL the time in sweets when they invade indoors.

For the Terro treatment you can keep it outside the heap.

Here is a link that might be useful: Fire ants in Oklahoma

The best place to learn about Imported Fire Ant control is from Texas A & M which has done the most research on this pest.
The presence of grubs, or any other insect larva in your compost can be an indication that the mix is too moist. The larva of these insects all need a fairly moist environment to hatch and live. There are those that will tell you that these grubs are helping convert your material to compost which is not quite true. They are digesting, and consuming, that compost Grubs and the larva of other insects that you can see do not belong in a compost pile.

Here is a link that might be useful: Fire Ant Control

Below is a prior discussion about grubs in a compost bin.

Here is a link that might be useful: Grubs in the compost bin