I found the following answer regarding import of related products (How to import related products in normal import process?). The answer suggests that it is possible to perform this type of import and recommends manually adding some examples via the Magento admin in order to see how the related fields are populated.
I performed a manual related product association and can see the related product in the back and front end, but upon export, the links_related_sku and links_related_position fields are empty.
I have since tried an import with an SKU in the links_related_sku field via Magmi, which was unsuccessful.
Am I doing something incorrectly or is the related products export/import "buggy"?