There are a number of studies that show the questioned effect that recruiters tend to rate those job seekers higher, which are more similar to themselves.
In this article Rivera finds that recruiters favor applicants who are culturally similar to themselves:
[...] evaluators constructed and assessed merit in their own image, believing that culturally similar applicants were better candidates. Finally, evaluators implicitly gravitated toward and explicitly fought for candidates with whom they felt an emotional spark of commonality.
D'Aveni looks at academia and find finds that:
There is evidence of homosocial reproduction. Senior faculty tend to hire junior faculty trained at schools ranked favorably by the same constituency as the schools where they themselves were trained, thereby reinforcing the strengths and reputations of their schools.
The effect is known as similarity attracts and is not only applicable to recruitment, but to many other areas of business. For example Westphal and Zajac find that CEO's tend to favor directors similar to themselves and that CEO's salaries are likely to be higher, if the board and CEO are demographically similar.
We propose that powerful CEOs seek to appoint new board members who are demographically similar, and therefore more sympathetic, to them. Using a longitudinal research design and data on 413 Fortune/Forbes 500 companies from 1986 to 1991, we examine whether increased demographic similarity affects board decision making with respect to CEO compensation contracts. The results show that (1) when incumbent CEOs are more powerful than their boards of directors, new directors are likely to be demographically similar to the firm's CEO; (2) when boards are more powerful than their CEOs, new directors resemble the existing board; and (3) greater demographic similarity between the CEO and the board is likely to result in more generous CEO compensation contracts
If you want to find more studies, you can start by searching for "recruitment similarity" on google scholar. That will give you a fair number of studies as a starting point.