Some disclaimer:
I have no experience with deb content and just looked into this out of curiosity. Also, since this looks like a problem with pulp_deb’s inner workings and not with Katello itself, you might have more luck reaching out on zhe pulp forum, though at least some pulp devs read here, too.
What I found:
Pulp is technically correct in stating that the repository you are trying to sync does not have a valid release file. According to the debian wiki, the “Components” field is expected to always be there, which is not the case for the repo you are trying to sync.
From what I understand, you might be able to sync the repository as a flat repository, see the Katello docs on how that might work. Though, I am unsure if this will actually work, since the repo uses the modern structure as far as I can tell but just ships broken release files.
Your best bet will probably be to ask the DUO people to fix their repository publishing.