Sim, eles propositadamente configuram isso. Se você assistir a primeira temporada do programa, o zelador nunca interage com ninguém, exceto JD. Há algumas ocasiões em que o um zelador está interagindo minimamente com os outros, mas se você examinar essas cenas, não está claro se alguém mais vê o zelador lá.
Na 2 ª temporada e em diante, eles deixam cair esse shtick.
Estados da Wikipédia:
As revealed in the DVD commentary on several episodes, the Janitor character was initially to be used as a figment of J.D.'s imagination if the show had been canceled during the first season or the first half of the second. This would have been revealed to the audience in the finale. ... Since the start of season two, Janitor has had encounters with most of the other regular characters. He has even had an entire episode ("His Story III") devoted mostly to him.