Yes, you can export boundary files from your current GIS and then import them for use in the UKHab Survey. You can import:
Shapefiles (in either EPSG:4236 or EPSG:27700) GeoJSON (in EPSG:4236)
In the Records view of your UKHab project in Coreo, select the Import button from the toolbar, choose the appropriate form to import your data into (almost always the pre-survey form) and then work through the import process. This also allows you to map any existing attributes if you wish.