There are probably plenty of Republicans in Congress who either don't agree with everything the Federalist Society stands for, or would get kicked out for being a RINO.
I'm sure there are Republican's in Congress who don't agree with the principles of limited Federal government and a judiciary that is restrained from adjusting the law beyond legislative intent.
The Federalist Society comes off as "anti-elitist," by advocating adherence to Constitutional principles. Those who subscribe to those principles are branded as "conservative" or "libertarian," and are assigned the political status associated with those labels.
I don't think the Federalist Society has an honorary program. It prefers members who make the affirmative effort to join, after thoughtful deliberation.