the majority of hoppers just have a paddles, or spindle that litterlaly jumbles the paintballs around (like the national lottery machine) and makes sure balls are going into the feed tube and not just blocking it.
the Halo, and Warp Feed, are slightly differant.
They use a force feed system, which allows them to feed faster, and more consistently. The Halo uses a roulette wheel style approach and the Warpfeed uses a waterwheel / cog to feel the paint. both exceptional hoppers, just very expensive.
the only marker on the market that definatly doesnt need a 3rd party hopper is the tippmann A-5 which has a built in force feed hopper system (the "cyclone system") i think.
that help?