Why yes you can and its really very easy.
Simply compile and export for Flex application and copy it to {eclipseGAEProjectName}\war\{flexName} or just put it in the root {eclipseGAEProjectName}\war\
See below:

OpenBD doesn't have BlazeDS remoting to Flex ( yet ) so I just used http service in this example but webservices will work aswell. Of course you could always add a crossdomain policy and use remoting back to a ColdFusion/Railo server if you need to and just host the swf on GAE.
Here is a follow up.
Here is a demo app:
This is actually sitting on Google App Engine just embedded into the blog. You can put in and RSS/Atom feed and it "should" load up in the DataGrid. By Default it gets ColdFusion Bloggers feed.
Here is the real link if your interested.
Here is the source its nothing fancy just a demo app.
BTW it is possible to get BlazeDS on GAE and I am looking in to this. From what I can tell its only amf with java right now though.
Here are my recent posts on Google App Engine and OpenBD ( CFML ):
Gettign Started with OpenBD and Google App Engine
OpenBD cfc's and Google Appengines Data store
Googles DataStore and how to view your data ( Enterprise Manager for GAE )
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