From MSDN:
Do not put files that are managed by extensible storage engine (ESENT or ESE) on a compressed drive. Placing a Microsoft Jet database on a compressed drive may cause write-through delays that can cause Jet database corruption.
RavenDB uses ESENT (Jet Blue) as its document store. So the answer is - DON'T DO THIS.
If you want compression, use the RavenDB Compression Bundle.