If anyone is still exploring the use of a profile name for the last secret, in the screenshots of the new version of MK:TE for gameboy, the profile they are using is "DRGNKING". I am guessing those screenshots came from Midway and not IGN.

I notice that in MKDA the profile name "DRAGONKING" fits exactly. I tried that profile name with the dragon icon and the example passcode and got nothing out of it.

I highly doubt it is anything - and I'm not wasting any more time looking for it, but if there are still some people trying profile names for codes, instead of just blindly guessing names, maybe you could start here.