Well, flymake looks like exactly what you need:

Flymake is a Vim plugin to perform on-the-fly syntax checking for the files being edited by using the external syntax checking tool (usually a compiler). It also highlights erroneous lines and displays associated error and warning messages. This plugin is a port of 'flymake-mode' for Emacs.

Just substitute the world "perlcritic" wherever it says "compiler", and BAM! The trick is configuring the output of perlcritic to look like the output of a compiler. The formatting capabilities of the --verbose option are designed precisely for this situation.

I know that people have successfully used Emacs' flymake-mode with perlcritic. So I gotta believe that you can make it work with vim-flymake. Let me know how it works out.

I know I can use perlcritic as "compiler" - that's how I use it with syntastic. :)

As for flymake, I don't think it's doing anything interesting. If you check the code, you'll see it start on file save, just like all other syntax checkers for Vim, and just run external checker using usual blocking system(), not in background. So, flymake is just basic version of much more advanced syntastic plugin.