Toe in or out KILLS tires, but BMW never designed a car with "heavy toe out" or any toe out at all.
Perhaps your mistaking the toe for the Camber.
There is a good deal of Negative camber which makes the wheel look like its in toward the middle of the car toward the top, and out more from the car at the bottom.
BMWs generally have a mild degree of toe in, meaning that the back of the wheel is out from the car a little and the front is in toward the middle of the car. Toe out would be opposite.
The combination that they have chosen is a huge compromise between the best handling they can give, quiet ride and tire life. Because it is still a "luxury sedan", it needs to still give acceptable tire wear andbe fairly quiet.
Toe in / Negative camber wont cause a shimmy unless they are uneven on each side.
a shimmy/ shake / vibration coming fromt he rear of the car could very well be an overlooked drivetrain issue such as an unbalanced driveshaft, etc.