I've used FMStudio with Dreamweaver CS 5.5 and FMSA 12 without issue, not sure about CS 6. Just need to make sure you use the API for PHP provided with FileMaker Server 12, not the version installed with FMStudio Pro.
This morning I received a reply to a Support Ticket I opened with FMWebschool concerning FMStdio Pro and DW CS6. They stated that FMStudio Pro will work with DW CS6 however it will be a couple of weeks more before they have tested all the available modules.
Good to know, hopefully they will post something on their site about it when their testing is complete although im not holding my breath on that.