I do not believe Casso was afraid of him why would he be?

He needs blood, Casso had plenty of shooters and he simply disposed of him.

He was the uncle of o e if the mob wives.

I don't think Casso feared anyone just perceived threats and if someone was a perceived threat they were exterminated.

Casso had the family behind him he could have taken out anyone he choose to and he did.

I mean he tried to whack the whole N.J. CREW.