RVM may be installed as super user. While it doesn't need to be, there are a lot of advantages to doing so (especially on a multi-user system). Any commands that come with Ruby (and associated Ruby Gems) should have their permissions set correctly to be run appropriately. Bundle does not require super user access to be used. It can run under a particular user, just as gem install can be local to a user or system wide when done with a full sudo.
RVM only manages your particular installs of Ruby, so that you can develop on multiple levels of Ruby- From RMI 1.8 and 1.9 to JRuby 1.6, et cetera. You may have different projects you are working on, and therefore need differing needs per project.
As far as on a server itself goes (assuming it's an external facing server with some kind of content on it), that just depends on the system administrators really. The use case changes somewhat. If you only need Ruby 1.9 on the server, there's really no need for RVM. Because managing multiple versions of Ruby is not required. So I would take that in to account when you decide whether to go system wide on a server itself.
Hope that helps!