Yes they can detect a proxy hit (from a transparent server). They will also detect a high bounce rate and that is no good.
The problem with most of your proxy lists is not the proxies but in the way they are tested. In most cases you are dealing with a Transparent proxy. In this case both credentials are present so it would not be in your best interest to use those proxy lists. It is true they will do ip bans but for the most part that isn't the concern.
What a lot of people forget is the largest reason botnets are still kickin so much butt is because a majority of the zombie computers are dedicated anonymous proxies, not transparent. These can be used to click on any link you want however you want. You can click adsense ads and so on. I know we like to think everyone is on broadband...most of the internet that makes us money is not. So every time their infected computer drops off and comes online we have a new ip address. We used to call dream of shell on linux in the early 90's, now we got these fancy networks.
So the short answer is yes, a proxy program will work to balance stats but no, proxies you find listed publicly will not work for this. Also, keep in mind that a lot of proxies also force content onto the visitor and that could effect your results.
If your in real need of a system like this your best bet is to use a fast IP range scanner and look for the servers yourself. A LOT of accidental anonymous proxy servers are floating around out there. Otherwise you need to turn a computer into a zombie and hijack the server. Good luck, though. MD5 hashes make it VERY hard to find the opp center for those bugs.
Another method that is kind of slow but works is the Mac swap. On an NT based machine you can change your MAC in registry settings. Disable and reenable the network connection and you should now have a new ip. Sloppy but if you need to balance some numbers to keep a robot from flagging you it will get the job done. Oh and that obviously wont work on a subnet.
wanna see this answered also