Yes, and Yes. They do block off the holes to the cam bearings. Roller cam bearings are fine with the splash of oil from the rotating assembly so they do not need the pressure fed oil. Now that the engine does not need as much oil you can slow down your oil pump (if running a dry sump or external pump) to save HP. If you are running a normal wet sump system then you don't need to run a high volume pump therefore reducing drag just like with the dry sump.
Now you do need to have the cam tunnel bored for them which usually costs a fair chunk. Usually going to roller cam bearings you end up going to a big core cam (55mm or bigger) which helps reduce the cam twist and flex from big spring pressures. Most do not go this route unless they have already done every other trick to make power and still need just a few more ponies.
While we are on the topic, I have a question. Is anyone making roller cam bearings for standard Chevy cams?
Paul