Answer: Photinia can be propagated by cuttings, although it may not be so easy to do at home for this particular plant. According to Michael Dirr's Manual of Woody Landscape Plants, take tip cuttings in late spring or early summer and use a well drained medium and mist; you will also need to use a strong rooting hormone. It should take about four to six weeks. There are additional instructions on how to take cuttings at the following web pages, you may find them helpful. You may need to cut and paste the complete url into your browser to make it work correctly.
As far as planting beneath the oak tree, it is generally not recommended to add soil or change the grading beneath these trees, or dig extensively in their root zone, as they are very sensitive to root disturbance. You might be able to plant a groundcover beneath it, perhaps something like Liriope or Confederate jasmine. Your local county extension and/or professionally trained nursery staff should be able to give you more specific suggestions based on a more detailed understanding of the planting area and your overall design goals.
Q&A Library Searching Tips