IIRC from your plant ID post, you have transplanted these smartweeds from a nearby location. If so, you are on the best path to success. I have found that local transplants have the best chance of survival. I have also found that the smartweed at my pond grows and spreads very well all on its own without competing with the rush grass and arrowhead. I hope the same for you. It is a nice plant that adds some color (my plants have reddish stems and small pink/white flowers),it does not get very dense or tall and stays in the very shallowest of water while living mostly on the bank. This makes me wonder if you will get much in the way of cover unless your pond level fluctuates...water goes down, smartweed grows at lower shore, then water level goes up covering the plants and giving temporary cover until the plant dies.
Look for some arrowhead, wapato, or duck potato (same plant just three common names) and see if it likes your area, I bet it does. This stuff can handle water level changes and mostly lives in 18 inches of water and less. It has a tropical house plant look to it and produces interesting flowers although not real showy. This plant would add diversity to your cover at the banks and takes up fair amounts of nutriets.
The best I can tell from your photos, you have dry-rooted your transplants. Meaning that you did not move any dirt with your plants from the previous location that kept the roots from being disturbed. Smartweed is pretty tolerant of being dry-rooted, but if you have trouble getting them to take in their new pond setting...try shoveling up a good wad of dirt around the root system when you dig them up and plant the dirt with the plants at your pond.
