Ho capito... ovviamente, subito dopo aver chiesto
;WITH XMLNAMESPACES (N'http://schemas.microsoft.com/dynamics/2006/02/documents/EntityKey' as DYN)
SELECT IDENTITY(int,1,1)
as 'ID',
c.value('(DYN:KeyData/DYN:KeyField/DYN:Value)[1]', 'VARCHAR(40)')
as 'JournalNum'
INTO #tmpBatches
FROM @ResultData.nodes('//EntityKey') t(c)