When using a subdomain with DMARC configured to send RUA, is it necessary to add DMARC reports TXT record?

If I send an email from [email protected] with [email protected] in the DMARC record of subdomain.example.com, is it necessary to create a DMARC reports TXT record (e.g., subdomain.example.com._report._dmarc.example.com TXT "v=DMARC1")?

No, not according to the RFC:

When a Mail Receiver discovers a DMARC policy in the DNS, and the
   Organizational Domain at which that record was discovered is not
   identical to the [Organizational Domain][2] of the host part of the
   authority component of a [URI] specified in the "rua" or "ruf" tag,
   the following verification steps are to be taken:

 1.  Extract the host portion of the authority component of the URI.
       Call this the "destination host", as it refers to a Report
       Receiver.

 2.  Prepend the string "_report._dmarc".

[2] https://www.rfc-editor.org/rfc/rfc7489#section-3