I'm not sure what "bog iris" is exactly, but we grow several types of irises - the same types I grow in other areas of the regular garden - in our bog, and they all survive the winter and come back bigger than ever the next year.

viega,
Louisana Iris is very cold hardy, loves water, or bog, or even planted in ground next to a pond. My friend had her louisiana iris just bloom, and she is in zone 6, she had a very bad winter last year.
Japanese Iris LOVES bog conditions. If you plan it in regular soil, you have to water every day to keep it wet.
SInce you are in zone 7, I would recommend you looking at a nursery for japanese iris, they are absolutely beautiful, they are very tall too.
I have both, they are not in the pond, I had the same problem as you with the dirt, so I planted them in the soil outside of the pond this year. Hopefully the louisiana iris will survive, I do water them every day though.
There are 2 different kinds of Elelphant ears. One doesn't like wet feet, the other one does.
You want Colocasia Esculenta for your bog area.
They can go in soil outside of pond too, but this EE does really well in water.
I have a gorgeous EE in a pot, with a deep saucer on the outside of it, keeping it real wet, and it is thriving.
They can take more sun than I thought too, but they must be kept real moist.
Good Luck.