UPDATE:
For RVM >= 1.11.3, you should now just use the rvm-capistrano gem. For older RVM >= 1.0.1, the answer below still applies.
ORIGINAL ANSWER:
Okay, though I still haven’t gotten a full cap deploy to work, I did fix this problem. The problem was Capistrano trying to use a different path for Bundler (and other gems) than the RVM paths.
Check your Capistrano path by doing cap shell, then echo $PATH. You’ll probably see your standard /usr/local/bin and /usr/bin, but that’s not where RVM has Bundler, et al., stored.
Edit your Capistrano config/deploy.rb file, and add the following lines, per these instructions:
# Add RVM's lib directory to the load path.
$:.unshift(File.expand_path('./lib', ENV['rvm_path']))
# Load RVM's capistrano plugin.
require "rvm/capistrano"
set :rvm_ruby_string, '1.9.2'
set :rvm_type, :user # Don't use system-wide RVM
That finally got Capistrano to see Bundler and start loading gems appropriately.