First, I'm not sure what it means to say that "There are no Jews in my basement" is unlikely to spread.

The Gestapo member is likely to have forgotten all about that specific lies by the time he finishes asking everyone on the block.

I can see an isomorphism (in terms of how the lie spreads) between "There are no Jews in my basement" and "There are no embezzled charity funds in my basement". Obviously this isomorphism doesn't extend to the morality of the lies, which makes it hard for me to see a connection between spreadability and immorality.

Disagree, the lies themselves are comparable, the difference in morality comes from the difference between the goals the lies are being used for.