What part of Zone 8? Some parts are hot and wet, others hot and dry. In my part it is not hot at all.

how big is the pot..

consider pot in pot ...

pots that get too hot.. cook roots .... and you lose ...

also.. you will need a good media.. not dirt ...

a pic of the spot would sure help me

ken

I am in Mississippi and the spot where the pot will be is facing the south. So it will be full,hot sun all day. That's
why I am being so careful about plant selection. The tubs are antique washing machine tubs, they are white and are
very large. I have considered several shrubs, perennials, and grasses. But since the site is next to my front door, I would really love to have something evergreen, if that is
possible.

If the tubs are antique it would make sense to use them as outers and put something else inside, like Ken suggests. You are in danger of rusting out the tubs otherwise. Plus metal tubs will get very hot.

I really appreciate you all taking the time to comment, but it
would have been nice if you could have actually answered
my question instead of concentrating on my containers.

How about oleander? Although it may be borderline hardy in a tub. But it sure can take the heat! Of course there's always Ligustrum japonicum, Euonymus japonica (Golden), Ternstroemia japonica (Cleyera), Pittosporum (might not be very upright though), possibly Podocarpus.

Rosemary?

Thank you for the good suggestions. Still not sure which
one I will use. Sorta leaning toward a dwarf butterfly bush.

The containers are important. If they get too hot, too wet, etc. they can have bad effects on your plants. Therefor you need to select a plant that is suitable for your containers.