Yeah, there are still lots of rubber balls to be found on the racks at many centers in my area. My guess is that most were just left behind by bowlers over the years.
I'm not sure of the specific impact on oil movement caused by rubber balls, but you have to figure that they were fairly non-porous, which would mean they'd have a tendency to push the oil around quite a bit.
As for using them on today's patterns, I never think it's a bad thing to have a very controllable piece of equipment in the arsenal. The only thing I'd worry about is the hitting power. Core tech. wasn't nearly as advanced back in those days, so you'd probably need to be just about perfect with speed, angle, and revs to get those balls to carry. Still, if you're on a grind-it-out type of pattern, I could see the merit in mastering the pocket with rubber.
