It is not clear if reddit has already engaged in this with Google, or if it is something that's only starting. However, as outlined in my post, they might have to consult with a DPA before engaging in this anyway, which I doubt they have done. So, no, DPAs are absolutely the right place to make that complaint.
Even if they hadn't started yet, might as well get their eyes on it, and force them to do it right from the get go (which they cannot do, as it currently stands).