GNU Global's distribution already has a couple of vim scripts that are pretty handy.
Look for 'gtags.vim' and 'gtags-cscope.vim' (the most adequate probably for what you want) in Global's installation directory, and just copy the one you prefer to your 'plugins' dir inside vim's config. The second script will do a
for you, which will route all normal cscope commands through the gtags provider and so will use GNU Global's DB when searching.
I prefer to simply use the :Gtags command directly though, which I find easier to use, but to each his/her own..
The plugin gen_tags can also help for easily rebuilding your source code DB directly from vim.