NO ... absolutely not.
EDIF has it's format publicly disclosed. There is no corresponding document for XDL ... so just producing XDL files with open source software would use material under the licenses NDA in voilation of it's terms ... specifically disclosing the file format without permission, and having developed competitive software after express limitiations against such an act.
As soon as you emit library blocks in an XDL file, you would disclose proprietary interfaces to their library too, in volation of the NDA protecting their documentation at minimum, if not proprietary device information from their databases.
Actually, the license gives you no right to disclose any internal data format, except the resulting programming bit stream.
So, unless Xilinx decides to publicly release these file formats, library definitions, and related material ... open source development in support of Xilinx FPGAs is off limits.
We have large companies like Sun that do give back to the open source community in the form of IP for use in the community. Open Solaris, Open Office, JAVA are reasonable contributions in exchange for the wind fall that comes from using open source products in a commercial product. That is the standard of conduct.
Not the highly restrictive licenses attached to every important Xilinx software tools, document, and interface.