As far as I know, none of the pre-DSpace 4 import mechanisms support ingestion of bitstream policies.
DSpace 4 AIP import and export supports the new, policy based embargo's. Reference: https://jira.duraspace.org/browse/DS-1514
This means that the METS export will now contain the embargo policy dates. For example, here is a policy where the bitstream will become available for public download on Jan 1st 2014:
<rightsMD ID="rightsMD_28">
<mdWrap MDTYPE="OTHER" OTHERMDTYPE="METSRIGHTS">
<xmlData xmlns:rights="http://cosimo.stanford.edu/sdr/metsrights/" xsi:schemaLocation="http://cosimo.stanford.edu/sdr/metsrights/ http://cosimo.stanford.edu/sdr/metsrights.xsd"><rights:RightsDeclarationMD xmlns:rights="http://cosimo.stanford.edu/sdr/metsrights/" RIGHTSCATEGORY="LICENSED">
<rights:Context rpName="" in-effect="false" start-date="2014-01-01" CONTEXTCLASS="GENERAL PUBLIC">
<rights:Permissions DISCOVER="true" DISPLAY="true" MODIFY="false" DELETE="false" />
</rights:Context>
</rights:RightsDeclarationMD>
This export was created using the AIP export
./dspace packager -d -e me@me.com -i 123456789/10728 ~/Desktop/export.zip -t METS