I have added a couple new links to theses:
Allison, Dawn Elizabeth. "A Study of the Priestly Christology of the Epistle to the Hebrews." M.A. thesis, Durham University, 1991.
Barbee, Dawn. "The Concept of Faith in Hebrews 10:32–12:3." M.A. thesis, Regent University, 2011.
I also came across this Greek thesis, which argues that Luke was likely the author of Hebrews:
ΠΑΠΑΔΗΜΗΤΡΙΟΥ, ΚΥΡΙΑΚΟΥΛΑ. "Η ΧΡΗΣΗ ΤΗΣ ΚΟΙΝΗΣ ΑΠΟ ΤΟΝ ΕΥΑΓΓΕΛΙΣΤΗ ΛΟΥΚΑ. ΜΙΑ ΑΔΗΛΗ ΤΑΥΤΟΤΗΤΑ: ΣΥΜΒΟΛΗ ΣΤΟ ΖΗΤΗΜΑ ΤΟΥ ΣΥΓΓΡΑΦΕΑ ΤΗΣ ΠΡΟΣ ΕΒΡΑΙΟΥΣ ΕΠΙΣΤΟΛΗΣ." Aristotle University of Thessaloniki, 1998.