I doubt the ivy is a factor in bumble foot,,,
I did want to bring a point to your attention. When your ducks wander thru the Poison Ivy, they may collect some of the oils that the ivy produces,, On their feet, and underside feathers. If you handle them, you can possibly get some that transfers to your skin.
Many peeps are not aware that even during dormant periods (winter) the Poison Ivy vines will give you a rash if you handle them bare flesh/hands.
Of course there is a percentage of people not affected by Poison Ivy. Read somewhere that it's about 15%.
My suggestion, if possible,,is to eradicate as much of that Poison Ivy as possible. I know the task in not an easy one. But possible to be under control.
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,and