Yes. Using XSplit with Loola is done through the XSplit built-in Virtual Camera (XSplitBroadcaster).
Note: XSplit only output video to its virtual camera. Capturing audio directly from XSplit requires to setup a Virtual Cable (Windows) or Soundflower (Mac).
Selecting the XSplit virtual camera in Loola is done through the video/audio sources menu:
In order to work with Portrait resolutions, you will need to add those resolutions first in XSplit:
Next, select the newly added resolution:
Lastly, select the new resolution in Loola: