Hi Chuck -
Filestream is supported natively by the Entity Framework, so as a supported type there shouldn't be any issues using it with DevForce. If the blob data is particularly large, you may start to run into WCF, IIS, router, or database timeout/size limits which may need to be adjusted. The first one you'd probably hit is in WCF, so you'd want to increase the send/receive timeouts on the CustomBinding for the client and server.
If the file transfer is particularly large, then you might consider going outside DevForce and building a separate service to process the raw bits.