I think you mean to be added to DEERS as a dependent so then you can be added to PCS orders. You do not need an SSN or tax number. I just added my non US spouse who is living in South America to my DEERS with a photocopy of her passport, National ID and an original apostilled marriage certificate. Next I will need to have her do a medical exam (using the form for those who cannot acces or get to a US medical facility/doctor) and submit that to EFMP. Once we both get to the foreign country I will start the I-130 and visa process as we will be overseas together for 24 months. I am hoping to use the DCF process and go through the Department of State instead of USCIS