Literal translation rule. In this sentence może=maybe is adverb.
On może być policjantem=He may be a policeman może=may is a verb
Because maybe and probably are different level of probability. Maybe=może, probably=chyba, prawdopodobnie
What about 'He might be a policeman' or 'He may be a policeman' as translations? Both of those would work for me. Or is there a different way of saying that in Polish?
I'd say that's "On może być policjantem". Seems almost identical, but "może" is a verb here, while being an adverb in the sentence from the exercise.
police officer is not accepted here while it has been every other time i have translated policijantem
In English "may be" is written separetly, if it`s a verb! Remember! please!
As an adverb it is maybe. As a modal verb it is may be. So i think the translation you have is correct Maybe he is a policeman. But similar meaning, He may be a policeman.