Use mouse scroll wheel in Vim
Using vim in iTerm 2 in OS X, you can
:set mouse=a
to enable scrolling with the scroll wheel, as well as selecting to enter Visual mode, etc.
If you use iTerm, you can simply execute the following command:
defaults write com.googlecode.iterm2 AlternateMouseScroll -bool true
This will enable mouse scrolling without having to add anything in your .vimrc.
You could try using https://github.com/brodie/mouseterm, which adds mouse reporting support to Terminal.