Just wondering if this is feasible?
The underlying http or soap request classes should work just fine (make sure to be on 10.2B02 or 03 and not using any .NET 4.0 Assemblies).
But the biggest plus of .NET's Web Service client implementation is the tools support in the visual studio or the SDK, that let's you import a web reference, parses the WSDL and generates a bunch of code that represents the data structures and methods of the service provider. You'll probably miss that in OEA very hard.
I'd rather build a custom .NET assembly that basically just contains the service reference and reference that assembly in your OEA project's assemblies.xml