So what I'm wondering I guess is is blockcypher mining and therefore (maybe) going to add the tX to a block if/when they find one?
AFAIK blockcypher don't have Bitcoin mining pool.
Or, are they just reporting that the TX has been "broadcast" (albeit just to their node) and no one else is picking up the TX to mine it?
Perhaps, but "broadcast" doesn't guarantee the other node accept the transaction.