Why? Finances for both are almost always completely separate for one another. From a fiduciary perspective Med Schools don't owe their undergrad students anything unless admitted. Most elite undergrads are just elite because they are piggybacking off of the great success of the faculty and graduate departments anyway and their commitments to undergraduate education are variable.
I imagine if there is a name on a rec letter or experience that the adcom recognize because of personal or institutional connections then that can add an additional level of credibility to an application but I don't think there should be institutionally specific bias.
That being said, there is definitely some of that bias present in med admissions, especially MD/PhD admissions. Top MD/PhDs usually take their own undergrads over other undergrads at disproportionate rates. 25% of all Harvard Mudphudders went to Harvard undergrad (a significant proportion also come from MIT which, let's face it, is also closely tied with HMS, especially HMS' dual degree program) and 80% went to just 5 schools, Harvard's peer institutions (HYPSM). Stanford, JHU, Penn are all the same although none of them are as egregious offenders as Harvard (JHU has like 12% JHU students, Stanford like 15% Stanford, etc). It's odd because it has been my experience that most science faculty look down on attending the same institution for undergrad and PhD to some extent.