The pronunciation of the Japanese ン changes depending on what sound follows it. Before a few consonants (I think
b,
m, and
p), it has more of an
m sound, and sometimes you'll see it romanized with an "m" rather than an "n." Live example at the Asahi Shimbun newspaper:
http://www.asahi.com/english/.
So "ramman" isn't really incorrect, although we would usually use "ranman" here on VGMdb. Since "TENSHINRAMMAN" is printed on the album, it's fine to use that as the display title and add "TENSHINRANMAN" as an alternate for searching, etc.