RVM will allow you to use any of it’s MRI/YARV rubies with passenger very easily.
Passenger is essentially ‘mod_ruby’ for both Nginx and Apache. You may select *exactly one* Ruby to run all of your Passenger Ruby applications with. If you need to run more than one Ruby interpreter then you should choose the most common one as Passenger Ruby. You then use proxy pass to external application servers such as Passenger Standalone, Unicorn, Thin, Mongrel, Mongrel2, etc… in order to accomplish running different applications under different rubies. For a full explanation of this (with pretty pictures!) see the post on Phusion’s Blog