Except for disk drives, Apple does not perform EMI susceptibility tests on its products.
We test the disk drives to ensure that they have sufficient shielding to maintain data integrity in a typical home or office environment. As long as the drives remain in their housings, you should have a great deal of latitude when positioning them, even without adding additional shielding. They should certainly be fine in any normal home or work environment.
As a general rule, in the abnormal situation where EMI is present, your monitors will be visibly effected long before there is any affect to data on your disk drives or other hardware.