User blog comment:Mathmagician/Patch 1.1 - Testing NPC Housing/@comment-98.231.84.96-20111218210318/@comment-4674838-20111218212407

The Hallow does not cause houses to be unsuitable. So if you're getting the unsuitable message, it's for another reason. If you're underground, it's possible that there's corruption nearby that you can't see. It might be worth digging around a little to see if there's any ebonstone hiding somewhere. And of course, make sure that you're building your house properly and all that good stuff.