UGS sells a JT translator for ProE2001.
PTC is a member of the JTOpen group, although it remains to be seen whether they will actually work toward better compatibility. Currently, ProE does not read JT files (even wildfire 2).
Teamcenter can be used to manage both ProE and NX togehter, and can build multi-CAD associative assemblies. The currentl limitation is ProE's inability to read the JT's, so NX has to be the top-level tool.
Terry