Using the Common library should be fine. Enumerations are serializable and the DataContract attributes are not needed.
See:
http://msdn.microsoft.com/en-us/library/ms731923.aspx
Enumeration types. Enumerations, including flag enumerations, are
serializable. Optionally, enumeration types can be marked with the
DataContractAttribute attribute, in which case every member that
participates in serialization must be marked with the
EnumMemberAttribute attribute
EDIT: Even so, there should be no issue with having the enum marked as a DataContract and having client libraries using it.