Why would they even need to eat? They're already "dead"
Well it ain't about if they need to eat, because they infact don't.
Some eat because they have constant craving for flesh n blood.
Some eat literal trash and rotten food just to ease said cravings.
Some eat because they wanna remember what it was like to enjoy something.
Some eat simply to ease their boredom.
Heck, some don't even eat at all!
Whatever the cause may be, the blood driven hunger would interrupt their lives eventually, it is inevitable. It would be up to them how they'll put up with it.