Is there a way to control the position of the wallpaper on an iPad running iOS9? On both the home screen and lock screen, I use portrait-oriented wallpaper images that feature full-length pictures of people. When the unit is rotated to landscape orientation, the iPad centers the image - cutting off the heads of the people in the images. 

There's a feature when setting the wallpaper image that allows one to shift the position, but you're effectively forced to set it for landscape and let it crop the sides when you switch to portrait. What I want it to do is align the top corners of the image with the top corners of the screen at all times, and have it crop the bottom when you switch to landscape.

Is there a way (hidden setting? third-party app? image-embedded meta-data?) to control the position of the wallpaper on an iPad running iOS9?
No; iOS does not provide any options or control for wallpaper positioning - you set the file and it does what it does.