When I'm running Nicodem, I am tending to move away from summoning as a key part of my plan. Regard the whole mechanic as a nice bonus when it comes off, but tend to rely more on Bolstering Nicodems minions as this is a more reliable aspect of his abilities.
I tend therefore to not worry too much about corpse counters. One or two for Mindless Zombie hijynx is nice though, and Mortimer works well enough for this, and offers some much needed mobility to the crew. I can see Rafkin and some dogs being a good solution, but I'm not sure I like him well enough to replace the Gravedigger, and dogs are something that has never performed for me at all. If I kill them myself I never get the crows to capitalise on the corpses, if I let them live they always disappoint. Generally speaking, I'd rather take something like a Crooked Man, where I can get more mileage out of the initial model then recycle it when it gets whacked by the enemy.
I love Killjoy with Nico. He's not cheap and will dictate a lot of your other points spend, but against the right crew he'll generate you corpse counters like nothing else.