I'm gonna assume potting mix would give it a better boost than the local soil would..
Be careful of assumptions. Often reality is way different to our preconceived ideas.
Potting mix is for growing plants in pots.
Often potting mix mixed in with garden soil will give good results but that depends entirely on the local soil and what it is lacking. The hard, red soil you describe will probably benefit from added organic material and that's basically potting mix. You could probably get a similar or even better result by adding animal manure, compost, etc but it depends what is easier to obtain. Whatever you add mix it with the excavated soil because roots tend to stop at a change of soil type. Having a mix encourages roots to grow out into the surrounding native soil much better.
Red soils are generally quite fertile with good nutrient so should grow good trees given water.
Be careful of digging holes in hard soils and clays then adding compost or potting mix. The holes can act as a pond and drown the trees during wet periods. Make any holes much wider than the plant to give excess water room to soak into surrounding soil. Larger hole will also give more root run before finding the hard native soils.
Good luck with the pomegranate.