Alan, you're correct; we did have this discussion at the last MCI, and everyone concurred that if the oak and/or tannic contributions were not readily obvious, and only served to enhance the overall profile of the mead, then those additions did not force the mead to be entered in the open category. This is consistent with the BJCP Guidelines (2008 version) which says, "If citrus, tea or oak additives result in flavor components above a low, background, balance-adjusting level, the resulting mead should be entered appropriately (as a metheglin or open...)." Now those are somewhat subjective criteria, as one person's "background" may be another's "in your face," so I would caution everyone to restrict traditional entries to only those meads that have slight oak or tannic characteristics, and a dominant profile from the honey itself.
That's the criteria for home entries; the commercial rules are somewhat different, but although I don't have the commercial guidelines in front of me at the moment, I think the discussion of oak and tannin is pretty similar in there.
