I'll be real honest right up front and disclaim that I DO NOT KNOW if I am speaking from a professional standpoint or a personal one with the following opinion:

I would never put anything on Ipe!

With that said, mildew resistant only means that they've put something in it to make it LESS APPEALING, not "proof". I swear I think anything can mildew. Second, while the rug is mildew resistant, the wet ipe that will be present after rain, dew, snow, will be less resistant and you are going to get discoloration from hell! If you were to put it out only when the area was in use and then put it away (PITA) it might be a nice accessory. I can just tell you that we have had many many issues when trying to restore ipe that has had just doormats placed, even out of direct sunlight. It is nearly impossible to ever even out the wood again (short of sanding all of it way down).

Celeste