They can only submit it confidentially. When you're on AADSAS requesting LOEs, they will ask you for your evaluators email (if they are e-submitting). From there, AADSAS will send them an email and give them instructions on how to submit the letter. This ensures you're not the one sending in the evaluation as well as maintaining confidentiality. Once they submit the LOE you'll get notification that it was submitted through your AADSAS portal.