Can you affect the Haunt roll with items, omens or other effects in Betrayal at House on the Hill?
Both the Rabbit's Foot and the Angel Feather have extremely generic text; the Rabbit's Foot says once during your turn, you may reroll one die; the Angel Feather says When you attempt a roll of any kind...

The only restriction I can see is that both the Rabbit's Foot and the Angel Feather must be used by the player who revealed the Omen card and is making the Haunt roll. Both of those items specifically restrict the affected roll to the owner's rolls. The rules state that a Haunt roll is made at the end of your turn, but that means it's still your turn.

TL;DR: Yes, the owner of those items may affect a haunt roll that the owner makes.