The current EAS protocol specifications (MS-ASCMD) 3.1.5.4 states that "Clients SHOULD NOT synchronize the Drafts folder." In fact, Outlook and Office 365 are explicitly blocking drafts sync. Microsoft is continually improving the EAS protocol, and if it is supported in the future, SmarterTools will implement it as well.
Here is an interesting MSDN community thread discussing this topic (especially read the answers from Microsoft).