I ran a different product using tick marks on a different server with 32Gb of memory and watched it process in Task Manager. The memory usage of FusionPro Server steadily increased until it reached the maximum memory assigned to the server.
At the same time, I monitored the text files being generated in the composition folder and the .msg file never changed off 0Kb, no matter how many times I refreshed the screen. From previous tests I saw that this file would at least jump to 2kb, as it recorded the job start, creator, computer name, working folder, temporary files folder, template file and input file, but in this case it hadn't even done that.
It does appear as if the graphics are being loaded into memory as the records are processed. This job has a print quantity of 45,000 units, which an imposition file of 36 units per page. The tick mark image is 13kb and if inserted per page, shouldn't be more than 16.25Mb, but clearly the memory usage exceeded more than this.