Archive Shuttle have the ability to collect metadata about items which are on hold in the source Enterprise Vault environment. This article explains more about this collection, and its usage.
The Enterprise Vault Collector module has been extended to collect ‘on hold’ information about each item that is collected from Enterprise Vault. This means that filters can be built to perform special processing for items that are on hold. For example, an additional per-user mapping could be made to make a copy of all of the legal ‘on hold’ items from a source archive into a PST file.
Note: Confer with Microsoft to determine whether the terms of your licensing agreement are impacted by the legal hold feature.