Gary Hudson said here that he believed that the Commercial Experiment Transporter (COMET), which failed to reach orbit on a Conestoga 1620 rocket on October 23, 1995, actually had received the first reentry license.
Looking around, I found this document about the COMET program: The Commercial Launch Industry, Reusable Space Vehicles, and Technological Change, Andrew J. Butfica, Business and Economic History, Vol. 27, no. 1 Fall 1998 (pdf). Pages 8-9 discusses the “License to Return” for the program:
> Ultimately, the OCST [Office of Commercial Space Transportation in Dept. of Transportation] licensed the COMET reentry vehicle as a payload on a licensed expendable launch vehicle. In this way, the OCST licensed the first landing of a reusable space vehicle before passage of legislation (still pending) that would empower the OCST to license vehicle landings.
So it sounds like the COMET got the first return license but Dragon got the first license actually authorized by legislation.