Must Gentiles Believe In Hashem

Rambam Laws of Kings (Ch 8 Law 11) כָּל הַמְקַבֵּל שֶׁבַע מִצְוֹת וְנִזְהָר לַעֲשׂוֹתָן הֲרֵי זֶה מֵחֲסִידֵי אֻמּוֹת הָעוֹלָם. וְיֵשׁ לוֹ חֵלֶק לָעוֹלָם הַבָּא. וְהוּא שֶׁיְּקַבֵּל אוֹתָן וְיַעֲשֶׂה אוֹתָן מִפְּנֵי שֶׁצִּוָּה בָּהֶן הַקָּדוֹשׁ בָּרוּךְ הוּא בַּתּוֹרָה וְהוֹדִיעָנוּ עַל יְדֵי משֶׁה רַבֵּנוּ שֶׁבְּנֵי נֹחַ מִקֹּדֶם נִצְטַוּוּ בָּהֶן. אֲבָל אִם עֲשָׂאָן מִפְּנֵי הֶכְרֵעַ הַדַּעַת אֵין זֶה גֵּר תּוֹשָׁב וְאֵינוֹ מֵחֲסִידֵי אֻמּוֹת הָעוֹלָם וְלֹא מֵחַכְמֵיהֶם.  What dos the Rambam mean, is the fulfillment of the 7 mitzvot not as a commandment of G-d in the Torah, a lack of fulfillment of the 7 commandments, or is it an additional law necessary to fulfill if a gentile wants a portion in עולם הבא?  If it is a lack of fulfillment of the commandments, why doesn't the Rambam say the gentile is held culpable for violating them, and if  not, then why is this a necessary condition to merit עולם הבא?    

It would seem the Rambam is saying that fulfillment of 7 mitzvot means the gentile is not doing anything wrong, but to merit to עולם הבא it is required to have a recognition in G-d that gave the 7 commandments.  See more about this and a twist of Rav Kook on the Rambam in 'גר תושב, חסיד אומות העולם וחכם אומות העולם.'  

The Rambam refers to a gentile who keeps 7 mitzvot but not as a command of Hashem.  Why does the gentile not keep them as a command of Hashem, is he ignorant of the fact that He commanded them, doesn't believe He did or doesn't believe in G-d?  Is belief in G-d a command upon gentiles?  There is somewhat of a discussion about this topic on forums, here and here.  It does seem to be the overwhelming opinion that a gentile must believe in Hashem and it is part of the prohibition against idolatry, blasphemy, part of the nature of commandments to mean there must be a Commander or maybe it is just a logical deduction.  Rav Moshe takes this a step further and says since a gentile must believe in Hashem, he is obligated to pray during an עת צרה as that is a demonstration of one's belief in Hashem.

This may paly a role in the question discussed by Rav Herzog (in teshuva to his son about joining Pope for anti-Communist declaration) if it is better for a gentile to be an ashiest or worshipper of avodah zarah.