It's not true. Valet only deals with dynamic sort start times and sort positions. It may make you an early or late starter on the sort, depending on the day. But it won't schedule you different routes.
It's also completely controlled by management. They have to go in and give training credit to anyone they want to be able to do a given sort position, aka offloading. If they don't give a particular employee credit for the training, that employee can't be selected by Valet for that sort position.
This way, they can really manipulate the program to better keep people in sort positions that make sense for everyone.