IMHO If there's no errata or appearance in Xlists you should be able to play it.
Aside from the rule of "cannot have 2 RB in play", I don't think there's such a card category as "only can be played if frodo is your RB".
I'm not relying on any crd phrase (and I don't think there will be any covering that for now), but based on when D decided RBs could not cancel anymore, in cards such as
Frodo's cloak or Elbereth whatever, you just ignored the cancelling part of the text.
In resume, I'm saying, nice combo and yeah go for that immortal frodo

(you would be ignoring the "Frodo is corrupted part") -it's not like you are getting away with something for free because after all you are adding burdens.