Hi fathernature,
Yes, during the application process, NUS always said that recommendation letters are not required, and if we really want to submit documents, they have to be related to what we wrote for the DA section (e.g. your CCA or internship etc).
NUS didn't explicitly say how documents can be submitted for DA. It is not even on their website. However, i called them and they said that there are 2 options - use form 2 which give me access to an application number, that is not provided if you you form 1, in which i will give my teachers so that they can create an account in a portal (normally only for people who are applying for scholarships, NUS claimed) using my application number and NIRIC, and their own NIRIC (I think) and upload their letters there.
By using form 2, i will have to upload a lot of supporting documents. NUS said that i can upload the letter or any document i think will be useful together with the documents (O and A level result transcripts, photocopy of NIRIC, PW results etc), but limiting to 2MB, which is kind of limited, even after i compress everything, as the must submit document already take up a lot of space. I submitted my boss' recommendation letter together with my other supporting documents. For this method, I suggest you choose the additional documents you want to upload wisely.
To future applicants, I have to say that uni application for people like me whose results dun really make the cut/a little bit off from previous year's COP, is very tedious. You have to find out a lot of things yourself if you want to try for NAA/DA (yes, you have to go beyond the websites and forums). For those applying for scholarship, i can't give you much info as i dont even dare to dream for it lol. Don't hesitate to save the office of admissions number in your phone to call them up when in doubt!