The RELO Integration does not include non-constituent records in it's matching algorithm, so the transaction will bring over a Constituent Update, in order to try and create a new constituent record.  To link to a non-constituent, the recommended best practice is to convert the non-constituent record to a full constituent.  Then, go back into the RELO plug-in and link to the newly created constituent record:
  1. Open the Constituent Information grid in the RELO plug-in
  2. Click on the transaction to check it out
  3. On the right-hand side, select Record Linking > Find Constituent (this will send the transaction through the matching algorithm again)
  4. Select the constituent from the results at the bottom
  5. Click Link Constituent
  6. Process the transaction as usual
  7. Process the Gift or Registration as usual
If a new constituent is created from the RELO plugin before the spouse record is converted, then the user should just update the existing spouse relationship record and link it to the newly created constituent record.  See How to find duplicate relationship records that already have a constituent record and link them together.