A 'church' wedding does not require being in a building, it's a matter of who the officiant is, what church he/she is a member of and the service used. Outdoor weddings are done all the time.
But in the case of the hilltop wedding, Look at the license:
According to this, the wedding was a civil ceremony that took place at city hall and Mike signed himself as a 'Divine Representor'.
To me, this means that the ceremony was strictly non-denomational. (But then, Mike is obviously a supernatural being, possibly an angel.)
Here's a link to a larger picture:
License