Originally Posted by PforPlatinum
T&C of $off certificate (PPDE) says:
3. Certificate may not be used or combined with any other travel discount or Onepass Reward;....
Thus I guess the answer is no.
The dollars-off cert should be OK to use on NW flights that are sold and ticketed as NW. Things might have changed as of late, but TCVs and discounted travel certs were freely interchangeable between the carriers since the alliance began.