No, you do not need to (and should not) upload these materials to Symplicity. OCI employers will only see your resume in advance of your interviews.
However, you should bring these additional documents with you to your on-campus interviews. We recommend that you bring enough copies of your resume, transcript, writing sample and reference list in case each interviewer you meet with requests them. Samples of these documents are available here. Make sure that your name is on each of these documents.
Please note that firms who are not participating in the on-campus interview program, but are instead conducting resume collections, may request some or all of these documents. Be sure to provide all of the requested documents for resume collections.