Q. On question 1989 you mentioned that" Rema (O.H. 156: 1) rules that Gentiles unlike Jews, who believe and serve G-d, are not proscribed from serving at the same time other gods, since they are not prohibited in believing in "shituf " or the partnership of the Almighty with other so called deities. Therefore, they are not considered idolaters." And that this is also the opinion of many Poskim.
Since they are not considered idolaters, are Christians Halachically allowed to pray to the other deities such as the son and the holy ghost?
A. Horav Yaakov Kamenetzky zt'l in Emes L'Yaakov (Vaeschanan 4: 19) addresses indirectly the question, and explains it by the difference of opinion between the Rambam and the Ramban.
The Rambam's opinion is that the gods and deities that constitute avoda zarah are only make-belief and only the false fruit of human imagination. They are totally powerless and worthless and therefore the ones who pray and serve them are not only transgressing a prohibition, but also wasting their time and effort.
However, Ramban's opinion in various locations (Vaeschanan 4: 15, Acharei Mois 18: 25, Behaaloscha 11: 16, et. al.) is that indeed Hashem granted powers to each one of those ministers and angels that represent each nation and therefore if they pray to them they have the power to help the people they represent. Still, he writes that those nations should pray to Hashem and it is prohibited for them to pray only to them.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a