I don't know how other proxy-blockers works, but webproxies are added manually into the dnsbl at tornevall.org (at least for the moment).
You can test ip's by adding them into this url:
http://dnsbl.tornevall.org/scan.php?ip=XXXX (where XXXX is the IP)
Like this:
http://dnsbl.tornevall.org/scan.php?ip=149.9.0.58
Edit: It seems that all those sites listed at privax is using the same exit...