To begin, both symbol and motif need to be defined in order to identify and understand how and why they are used.
Symbol: A person, object, image, word, or event that evokes a range of additional meaning beyond and usually more abstract than its literal significance.
Motif: A central or recurring image or action in a literary work that is shared by other works and may serve an overall theme.
Therefore, a symbol can appear once and remain a symbol. A motif, on the other hand, is a symbol which appears repeatedly throughout the work.
In regards to the symbols/motifs in Bruce Dawe's poem "Homecoming," the symbols seen all speak to the motif of death.
Dawe's poem was "written as an elegy for anonymous soldiers" in the Vietnam War. The poem tells of the process with which dead soldiers were "processed" for their return home. The overwhelming symbol in the poem is the use of the word "them." "Them" are the dead and unidentified soldiers who are being picked up, brought in, zipped up, tagged, and named.
they’re picking them up, those they can find, and bringing them home,
they’re bringing them in, piled on the hulls of Grants, in trucks, in convoys,
they’re zipping them up in green plastic bags,
they’re tagging them now in Saigon, in the mortuary coolness
they’re giving them names, they’re rolling them out of
the deep-freeze lockers
Therefore, the symbol of "them" represents the numerous unidentified bodies. These bodies are then identified as representing the motif of death.
An engaged reader can see that Dawe is not pleased with either the treatment or the war itself. His tone is rather angry (overly objective which could allude to his actual subjective nature), while the rhythm matches the drums heard in war times.