I am from same embassy as OP and yes you do have to send originals to nvc . By original I mean original birth certificate, marriage certificate ,translated certified English translation of nikah Nama , original certificate ,every document needed . I will repeat again send originals don't take a risk .even on interview letter there's a check list wihicj says "original recieved " .Embassy always return originals and keep copies but if you are worried you can state in your cover letter that you request them to return originals at the time of interview and keep copies which they are eventually gonnna give them back