both the film & the band seem to be at least related to the comic book that influenced them, imo.
basic examples:
'shadow gallery' is the name of the character's hideout.
the character is named 'V' and coincidentally spent a long time in a prison cell labeled 5 in roman, specifically 'room v'.
the character's goals are to overthrow a tyrannical modern government.
unlike that ridiculous joke thread relating symphony x to various things, these are solid evidence as well as the concepts being similar. i would easily bet money that the band used the comic as an influence. it'd be a typical prog rock thing to do.
want more evidence? look at the song titles, and even some of the lyrics.