You can accomplish something similar with listchars and list:

  set list
  set listchars=tab:»·,trail:·

It will not give you a file-wide warning but it will make tabs stand out (along with trailing whitespace).

Not much help if you actually want tabs, granted.

here's a blog post i found that does what you need (http://got-ravings.blogspot.com/2008/10/vim-pr0n-statusline-...)

and then you can replace one of the airline sections with it.