Hi Brad,
I could not find any documentation, but after a quick test, this appears to be supported. I was able to replicate an SDE feature class with attachments to another SDE geodatabase. I am running:
ArcGIS 10 SP3
ArcSDE 10 SP3
SQL Server 2008 SP1
Are you receiving any error messages?
Here was the test scenario:
1. Register SDE feature class as versioned
2. Create attachments for the feature class
3. Add Global IDs to the feature class
4. Create the replica
5. Add an attachment to a feature
6. Synchronize
I found that if the attachments are created before you add the Global IDs that when you add the Global IDs to the feature class, the related attachment table will receive a Global ID field as well. If the Global IDs are added before the attachments are created, the related attachment table will need to have Global IDs manually added to it.
Check to make sure your feature class and attachments table both have the Global ID field.