Just go into the Extensions window and then Vimium preferences; you can add this vi page to the list of "excluded URLS".

If it was done in a similar way to vimperator there should be a passthrough mode (ctrl-z in vimperator)

In vimium you can press 'i' to go into 'insert mode (sort of)' which works similarly (albeit not as well as) vimperator's passthrough mode.

Adding the exclusion is probably the best route though.