Any word can be a name, and any spelling (e.g Deborah used to be the accepted spelling, but if yout parents named you 'Debra' then that's the right way to spell YOUR name).
Melodie - could be misheard as Melanie, but why worry
It seems to be the latest fashion to change the spelling of names, especially y - ie. As for the name Melodie, I really like it, it's hard to find names which aren't common or so strange that you follow the trends of the celebs.