If it was me, I would not use a petroleum based product to lube a plastic roller. First, as you point out, not knowing exactly what kind of plastic they are, you don't know what effect the oil/grease will have on them. I have tried "oiling" plastic before and regretted it each time. Second, oil is a natural dust/dirt/sand attractant, that will help grind your plastic surfaces and can get on anything that comes in contact with it. BTW, gear oil, IMHO, is one of the nastiest things ever producced by mankind that wasn't radioactive. It stinks and really attracts the yick. Vegetable oil will just get stickier and add to your problem.

If I had my choice of anything, I would use a CRC dry lube spray, McLube sail track spray, furniture polish spray, mineral oil or maybe even compass oil which is supposed to be more like mineral oil. With any option but dry lube I would also try one roller as a test.