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RAW, I think yes. However, as Oracles do not need to worship a specific god (and technically, non-Golarion clerics as well), the real question becomes, what is the "holy symbol". The clerics who don't have a specific god says to work with the GM, so I'd say RAW you need the divine focus and that divine focus uses all the rules for holy symbols, but in form must be something that represents what you revere.
Of course, you could take a hyper-literal RAW interpretation and take the position that RAW, you only have to be "able" to present your holy symbol and the rule doesn't actually state that you "must" present your holy symbol, but that's the kind of interpretations (I presume) that drive developers up the wall.
RAI, I don't know.
What to do? -- I don't think it's a big deal if a GM lets a Life Oracle with the Channel revelation channel without any divine focus. Personally, I've played a Life Oracle and totally disregarded the whole presenting of the holy symbol when channeling because I didn't notice the discrepancy like you did.
Also, whenever one class has an ability that references another class, the GM sometimes has to make interpretations that make sense to the play group (i.e. little adjustments to get things to work right).