Rutherford was definitely opposed to the League of Nations, but in this he was not alone. Wilson was one of the League architects, but there was such resistance to it within the US that the US never joined it.
I'd be interested to know more of why Rutherford opposed it, likely was more of a personal reason. I wonder if it had anything to do with the fact that William Jennings Bryan supported Wilson's efforts to get the US into the League. Rutherford had campaigned for Bryan back in the 1890's before becoming a Bible Student; maybe he wanted to take an opposition stand to Bryan.