My friend and I were discussing the issue of whether or not a male ger could become a rabbi. I’m pretty sure a male ger can, but my friend says they can not. Can you please clarify this for me?

A Ger may perform all of the common functions of a Rabbi including deciding all matters of Halacha if he is competent. There are certain limitations of a ger participating in certain functions of a rabbinic court (e.g. for Chalitza) but a ger may serve as a halachic advisor for a court.