I don't believe there is such a list, some unsupported elements that i know of are:
Also make sure that the wsdl contains a schema that describes the elements of your operations, i found that some wsdl's do have this.
EDIT:
Another thing is that sometimes WSDL's can be imported if you tweak them a little before you import. i.e. remove the choice element and replace them with a sequence or remove the any element and replace it with a sequence and with its child elements.