The release notes aren't clear on if / how you can provide configurable write concerns for mongoimport - see: http://docs.mongodb.org/manual/release-notes/2.2/#write-concern-support-for-mongoimport-and-mongorestore

The command help and main docs don't seem to correlate - http://www.mongodb.org/display/DOCS/Import+Export+Tools#ImportExportTools-mongoimport