"It’s a safeguard for the creep of subjectivity."
This is a slightly odd phrase indeed, but I'm quite confident you can interpret it as:
"It [the test of replicability] is a process that prevents subjectivity [opinions and views] from being accepted [over fact]."
In the context of the article, for those who haven't read it, the quote reads:
First off, subjectivity is the act of being subjective. Something subjective is based on opinion or belief, and is the opposite of something objective, which is not based on opinion, and is a fact based, repeatable observation. For instance:
is subjective, as it's arguable that the picture does indeed look nice in that room (it's an opinion!)
is objective, as the picture is inarguably within the room.
In this context the verb "to creep" has been used to refer to the encroachment of subjectivity into the scientist's experiments. If the results of an experiment can't be replicated independently by several teams of scientists, it cannot be said to be objective.
Therefore the author is saying that replicability is important to these scientists because it means that the results remain objective.