FFIX's characters have last names as well(not as if it counts because it's not Tetsuya's work). And the reason some names are meaningless is because the characters are named after a certain someone instead of being an original name.
And one more,
Rokkuhato=Lockheart because the R sound in Japanese actually sounds like a L sound. They don't have a singular K sound so they took the nearest, the KU sound. HEA=HA, done. They also doesn't have a singular T sound and therefore they took the nearest, the TO sound. Though the names are spelled in katakana, they actually follow the sounds from the hiragana sound table, aka the original one. So, they had tried their best to pronounce it correctly already.
So, it should be about this: LO(RO)-KU-HA-TO---> LOKUHATO. Close enough. Be satisfied.