Can I use XML API Sync in Housing Market CRM and on the portal?
Yes. It is one subscription and one feed: a feed you set up in one appears in the other.
XML API Sync is under API/XML Sync in your portal dashboard and under XML API Sync in Housing Market CRM. Both show the same feed, the same mapping and the same results, and you subscribe once, for 29 USD per month, in either place.
The listings it imports are your portal listings. In Housing Market CRM they appear with your other portal listings, marked as managed by your feed, so a change you want to keep is best made in your own system.