The futur antérieur can have two different uses:

• Temporal function to express a completed future action:

  Je t’appellerai quand je serai arrivé:

• Modal function to express probability or supposition in the past:

  Il n’est pas encore arrivé, il lui sera arrivé quelque chose.

This is what is expressed in the sentence in your question.*

The use of the futur antérieur is enough to express probability, using an adverb to reinforce the degree of probability (peut-être, certainement, sans (aucun) doute…) is only optional.

If we compare with the use with the passé composé:

• Ça les a peut-être fait hésiter un peu. → peut-être is used to show the event is hypothetical.

• Ça les aura fait hésiter un peu. → the futur antérieur is used to the event is hypothetical.

We would use the conditionnel passé to show an even greater degree of uncertainty:

• Ça les aurait fait hésiter un peu.

in these last two sentences peut-être maybe just adding a little more doubts, maybe!

Further reference Le futur antérieur de l’indicatif, niveau B2

*_{In English, this probability is expressed by a modal verb ("must" "might"…) (It must/might have made them hesitate).}