I was wrong in my post above.. but .... I think I did find out how to report to alexa although you will need to modify pliggs navigation bar slightly.
Instead of using mydomain.com in your pligg navigation try using
Code:
http://redirect.alexa.com/redirect?{$my_base_url}{$my_pligg_base}
This should push every URL through alexa and record the pageviews.
Another neat thing is that you can use this when posting your link elsewhere where the URL is not shown.. For example: in my signature below check out the scooptube link.
I'm currently testing this out and will let you know the results.