Perhaps 'Object as Camera' should be called 'View from Object'. The selected object does not become a camera, with all the attributes of a camera, such as focal length and sensor size. You can dolly it, but you can't zoom it. Nor can you, for example, set your object to give you an orthographic view.
The perspective transform seems to be hard-coded for convenient use in the viewport, the only accessible variables in it being the location and rotation of the pivot-point of the object. (Perhaps someone who knows where to look can confirm this, and tell us what the field of view is set to). The function seems only intended to help with various tasks in the 3D View, such as aiming lights.
Maybe your best option is to create a real camera and copy the transforms
of your object to it, and/or or put a Copy Transforms constraint on it.