Can webMethods import mappings generated from third-party mapping tools? If so, complex mappings generated by which tools can be used.

Integration Server can use XSLT. It doesn’t “import” XSLT files per se, but uses them directly. There is a service you call, specifying the source and the XSLT to create the output.

If by “import” you mean creates FLOW MAP steps from some external representation, there is nothing I’m aware of.

Thanks Reamon. By import I mean creating Flow map steps from importing a file genetrated by the external third party tool.

Liaison Contivo (http://www.liaison.com) will generate Flow (or Java I’m not sure) mapping services for webMethods.
I have not used the tool myself, but have spoken to people who claim it works pretty well.