DevForce uses somewhat different means of looking for the methods marked with the AllowRpcAttribute vs. an implementation of a custom EntityServiceApplication.
Methods marked with AllowRpc aren't actually probed - the type and method information provided in the InvokeServerMethod call is used to search for the method. The assembly is loaded if necessary, but it's assumed to already be in the bin folder. If you add the assembly name to the <probeAssemblyNames> somewhere in the config this will usually just mean that the assembly has already been loaded (usually when probing for other reasons) before the type and method are reflected.
Probing is used when looking for a custom EntityServiceApplication. Here only the top-level (as opposed to EdmKey-level) <probeAssemblyNames> are searched. So your implementation should be found if you add (or move) that <probeAssemblyName> element to the top-level. (You can use the Configuration Editor if you need help with the elements/attributes defined in the ideablade.configuration section.)