The criminal justice process begins when a crime is committed and ends when corrections are presented to the individuals involved. Everything that happens in the courts up to sentencing is all part of the criminal justice process. According to the FBI, pretrial hearings in front of a grand jury are, in fact, part of the criminal process. Grand Juries are not always used; however, it is important to know they are not part of determining guilt or punishment.
The grand jury has quite an important role in the criminal process: prosecutors will usually work with a grand jury to decide whether to bring criminal charges or an indictment against a potential defendant -- usually reserved for serious felonies. In summary, a Grand Jury will determine if there is enough evidence to convict an individual for a crime.
To abstractly respond to your question, Grand Jury hearings are in fact part of the criminal justice procedure. Although everyone will surely have their own opinion on the matter, just know that if it is part of the process in furthering a court case, then it is part of the criminal justice process.