Do Android Stock Browser, Firefox Mobile and Opera Mobile use proxy server to perform rendering
In Opera Mobile, you can enable Opera Turbo to use the same proxying technology as used by Opera Mini.

Android Stock Browser does not use compressing proxy at all and I believe neither does Firefox Mobile (though given that Firefox Mobile has plugins system there might be a plugin for that).

Several lesser known browsers in the Market does use similar proxying technique, but I can't recall off the top of my head which ones though.