A very funny, over the top novel, but about what?

Did look up Ulms on Wiki and unsurprisingly learned that this cult or sect is something Joshue Ferris invented for his novel To Rise Again at a Decent Hour, but on the other hand the Amelikites or however you spell that are actually in the OT - as I'd thought - I remembered reading about that incident in which the tribe decided to convert to Judaism and went through the various rituals including circumcision of the now-adult males and the Jews attacked them while the men were all laid low recovering - not the proudest moment in Jewish history, I'd say. So that part is real or at least is chronicled as such - but the idea of a small surviving sect from the tribe is Ferrris's fantasy - and I'm just not sure how to read this novel or what to expect from it. Yes, it's very funny at times and well written at all times - but are we supposed to see the narrator as a disturbed possibly delusional man who believes he's a member of this long-lost tribe, or are we to see the tribe of Ulms as real - and if so what's the point there? It's obviously a satire and a send-up, but to what end? Ferris's first novel was, like this one, exuberant and over the top and I did enjoy it pretty much - the story of a PR firm in Chicago undergo various layoffs and cutbacks and the guerrilla actions initiated by one (or several?) disgruntled employees - which in the broader sense was an attack on corporate America - but in this novel what is the aim, what is the target?