It should help but won't be adequate by itself. You'll need to water heavily at least out to the dripline. Assuming you are talking one pot inside the triangle of trees it's just not nearly enough water.

I would think it would inhibit the trees from sending their roots outward and thus make them less secure and stable in the ground.

I won't have a drip line. At least I hadn't planned on one. Maybe I'll rethink but I was concerned with chloramine in the water killing microbes and trees are spread around a half acre. Soo, A 1.5 gallon olla buried 12" sounded like a good idea to me. I can supplement water manually on a daily basis if need be during the summer months from a stock tank that has aged water in it. I'm retired so being a water jockey is ok.

I hadn't thought about stability itilton. Good thinking.

Those three trees on M7 in 5 years will probably use 40 to 60 gallons per day. Maybe you'll get half that in rain but not always.

Thanks fruitnut. Obviously I need to rethink. First off, I'll need to plant the three trees with normal spacing. They would be competing with each other too much for resources in a 3 in 1 hole design. Second, I may need to go with a drip line. Cheers.