In Judaism, prophecy means to communicate the direct word of God. Someone who does the things that you mention might be a great person, but that is simply a different thing from prophecy.
The Bible lists 55 Jewish prophets, although the Talmud (Megilla 14a) states that there were 1.2 million Jewish prophets, so prophecy was not limited to those prophets mentioned in the Bible. The Talmud explains that the vast majority of these prophets' messages were only relevant to their own generations. Only the messages that were important for the future were preserved in scripture. So the answer to your title question, "Can non-Biblical figures be considered prophets?" is "yes."
However, being an "upholder of the law" and bringing a community to religion are not the same thing as prophecy, and they are not necessarily even required qualifications for it. God can grant prophecy to whomever he chooses. An example to prove this is Bilaam who was an evil man, but was nonetheless granted prophecy.
In summary, prophecy and being a great leader are simply different things. There is definitely a correlation in the Bible between great leadership and prophecy; however, prophecy ceased to occur long ago even though there have been many great leaders of the Jewish people.