Per DL's website, business class pax now are relegated to the Menzie's lounge in AMS. Kind of a bummer and not sure how well that is controlled. Same for Syteam Elite +. Skyclub members are apparently the only DL passengers allowed into lounge #52.
The MSP lounge on the C concourse is nicer and newer than the one on the F/G concourse.
Unless the rules just changed, I don't think this is accurate. I used #52 last Wednesday with no trouble at all...