Okay, a quick test of a simple solid shows that one can in fact import the iges into UG and sew the surfaces together to come up with a valid b-rep solid. With more complex solids, or assemblies it could become prohibitively time consuming, as each surface needs to be selected. In addition, with complex models, blends may not touch, and the sew will fail.

I notice that Solids++ offers a step translator. That would be the only translator you really need, as every major cad system supports step, and the output from step can be a valid b-rep solid.

Here's a picture of the imported, sewn solid, shown in section...