It would be interesting if a large company that could afford to do so (say, Google) made an attempt to experimentally test that question. It'd take some thinking to design a useful study with some sort of blindness, but something along the lines of: have everyone do the technical interviews, but then for some subset of interviewees, the final decision-maker chooses whether to hire or not based on a coin flip instead of based on the interview. Then assess the performance of each group of hires a year or two later.

Disclaimer: may or may not be legal; I'm no employment-law expert, so have no idea if "not hired due to coin flip" would be a grounds for suing.