On the one hand, a lot of Ogham “mythology” is drawn from Robert Graves, and we’ve discussed the issues with this before. Moreover, there’s not much to back up any pre-Christian use of Ogham in Ireland, or the parts of Britain whither it spread. On the other hand, however, Celtic cultures didn’t just stop in the Iron-Age, sub-Roman age or Medieval period. I don’t see anything wrong working with Ogham as long as it isn’t passed off for something it isn’t.
The bardic cultures of the Celtic peoples were, in a sense, a continuation of those cultures that had birthed or nurtured druidism, so I’d say take the Ogham for what it is and work with it, but don’t try to turn it into something it never was.