I would say we don't have accurate enough measurements or an accurate enough theoretical understanding to know how many micro-black-holes we should expect to see from cosmic ray collisions, on the assumption that none of them ever evaporate, or to be able to measure how many there actually are, so as to be able to compare the two numbers to see if there's a significant difference. In principle this would certainly be a good experimental test for the existence of black hole evaporation; I just don't think it's a test we can make with any confidence now or in the near future.