There was a lot of talk about eliminating the pre-match process this year, but as far as I can tell, it has not been implemented. The NRMP web site still classifies DOs as Independent Candidates and I cannot find any restrictions on pre-matches for this group. The following is from their section on FAQs:
I've signed a contract outside the Match. What happens now?
Under the terms of the Match Participation Agreement, an independent applicant who accepts a position outside the Match must withdraw immediately. Failure to do so is a material violation of the Agreement and will be investigated by the NRMP in accordance with the Policies and Procedures for the Reporting, Investigation, and Disposition of Violations of NRMP Agreements. Penalties may be levied if a violation is confirmed. No applicant can withdraw from the Match after the rank order list deadline.
This seems to allow pre-matches at this time.