Can I glue D rings to the back of a frameless mirror
Can you? You could... but I would advise against it. 

A better option (depending where your skill set lies) is to make a frame for it, or glue the mirror to a piece of wood that you can then attach fasteners to. You could use a piece of plywood for instance, which is cut smaller than the mirror (2 inches on each side is probably plenty) so you don't see the edges unless you're right against the wall. Attach the D-rings to the plywood with brackets (like these)