My understanding is that these letters of recommendation are required to enter most medical schools.
They may, or may not help. Of the MD's I know personally, the opinions they expressed as to who got into Med School were based on grades, scores and the personal interviews. However, undergrad grades and scores on the MCAD are going to be the primary determing factor, unless you are a minority (but that's an unrelated topic to this article). The overall feeling was that unless the letter of recommendation was from a REALLY well placed researcher (Nobel winner for Cancer research as an example) the letters were of little significance.