Let me start my answer with a little bit of background of Reiki terminology.
It appears that the term Reiki “master” came into use in the late 1930s from Mrs. Takata, a Japanese American, who learned Reiki from Chujiro Hayashi (one of the prominent students of Mikao Usui, the founder of Reiki).
Reiki is a Japanese healing art, and Reiki terms had to be translated from Japanese into English as Reiki was introduced to the Western world. So the original Japanese term for Reiki “Master” was actually Reiki “Shihan”.
The word “Shihan” is probably best translated into English as “teacher” (also “master”, but used in the same connotation). The term “Shihan” is not exclusive to Reiki, and it is widely used in the Japanese martial arts as an honorific term for an expert instructor or a “master teacher”.
The term “Master” in English has many other meanings and may not convey the true sense of the original word “Shihan”. Over time, it has been used more and more loosely in many Reiki styles, becoming probably the most commonly utilized term when referring to a Reiki practitioner who may or may not be a Reiki teacher.
Now back to your question.
Reiki Shihan (vaguely translated as “Reiki Master”) is a real title that is used for someone who has completed the teacher’s level of Reiki training. So yes, it is a degree of Reiki training; however, it is not a university degree, if that's what you are asking.
As far as the term “Grandmaster”, it appears to be a vague translation of the Japanese “Dai-Shihan” (someone who is considered to be an expert teacher and who can teach more advanced levels of Reiki). Of note, there are very few actual real Dai-Shihans (“Grandmasters”) in the world. For example, in the traditional Japanese Jikiden Reiki style, as of today (2017), there are fewer than two dozen teachers of that level of training and expertise (Dai-Shihans) total in the world.
So to answer your question, Reiki Dai-Shihan (loosely translated as the “Grandmaster”) is a real level or degree of Reiki training and expertise, but it is not a university degree.