I had a roller go flat and it wiped the cam in about 8,000 miles, that was the old style classic rollers installed some years ago. I understand there are now '
oil pressure' fed rollers that reduce the problem of lack of oiling on a street car. The old method relied on 'splash' and high rpm to get the job done. I would GUESS the new pressure fed rollers require an engine that can also run hydraulic lifters and this is how they are pressure feed?
Original side oilers could NOT run hydraulic lifters, as an example. I am currently running flat tappet standard lifters even though my side oiler block (1968) could run hydraulic lifters or pressure fed rollers.
NOTE: These modern rollers are comparativly expensive and most people opt for hydraulic rollers instead, which are also 'not cheap'. Classic flat tappet solid lifters are a bargin, all things considered.