I think he's pretty safe for turns 1-2 in most cases, to collect body parts as much as possible and then summon the zombie horde. After he drops the initial batch he becomes less of a target. Like you said, he can no longer gain free body parts from Nicodem after he manifests, so more than likely he'll scoop up the odd corpse counter he is able, use fast where possible, put up his Hard to Kill bubble, etc. Will he get picked on? Yeah. But if he can put 5+ mindless zombies on the table the turn Nicodem manifests (ie in addition to having the same ss size force you started with or more likley even higher) then he's paid for himself.
I'm not seeing how Mortimer and Molly can reliably put out 3-5 corpse counters? Mortimer casting Exhume is dodgy at best, and may require a 7+ from your hand (not always plentiful) and quite possibly a crow to boot (also quite likely a limited resource). Expecting to get it to go off 5 times between the two of them and her totem is asking a lot. Or am I totally missing something they can do? Entirely possible....