yes, Data Assist is compatible with DW5.5
see the known issues section of the data assist download center page for a fix to the problem you are having.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.