I've never seen Ipe milled into or used as an exterior siding.

My main concerns would be water seeping into the horizontal 1/4-inch gaps, which types of fasteners to use as well as expansion and contraction of materials. Maintenance can also become an issue if trying to preserve the natural color and beauty of the wood. Fire and building codes may also prohibit the use of non-conforming siding materials on residential and commercial dwellings.