In theory, when context isn't making it clear, you need to use a pronoun for 3rd person, because verb on itself can't indicate gender in present tense…

In practice, it is rare in actual spoken language, because it is very rare to not have some context then. So, setting the rules aside, I think it should be accepted(even if the default should be "One podróżują razem" and "Oni podróżują razem"), so please report it.