I am no expert, but I do have a family member that has Meniere's Disease.
Unless someone knows otherwise, Meniere's can not be secondary to Tinnitus, actually Tinnitus would be secondary to Meniere's.
I posted the VA rating section for Meniere's here for you.
6205 Meniere’s syndrome (endolymphatic hydrops):
Hearing impairment with attacks of vertigo and cerebellar gait
occurring more than once weekly, with or without tinnitus............................... 100
Hearing impairment with attacks of vertigo and cerebellar gait
occurring from one to four times a month, with or without tinnitus.................... 60
Hearing impairment with vertigo less than once a month, with or
without tinnitus........................................................................
............................ 30
Note: Evaluate Meniere’s syndrome either under these criteria or by separately evaluating vertigo (as a peripheral vestibular disorder), hearing impairment, and tinnitus, whichever method results in a higher overall evaluation. But do not combine an evaluation for hearing impairment, tinnitus, or vertigo with an evaluation under diagnostic code 6205.
It is my understanding that Maniere's Disease in and of itself actually means "A disease of balance (vertigo) with possible hearing loss, and other ear related issues, with no other identifyable cause". It is usually diagnosed by ruling out other balance diseases that have specific symptoms and causes. I can't help you with a possible service connected cause.
I hope this helps some.