Yes, you can integrate OTM with external web services. The restriction is that OTM will only pass out G-Log XML, so you'll need an integration engine (if you're running MS software - this may be BizTalk) to accept the request and transform it into the format you need for your end system(s).
The basic steps are:
- Create a Web service definition in OTM
- Associate a WSDL file with this web service that describes your endpoint.
- Create an External System in OTM, which uses this web service definition for transmission
- Associate this external system with your agent or action that is going to send the integration transmission (planned shipment, order updates, etc).
I don't believe this is fully documented anywhere, though I'd recommend checking the OTM Integration guide.
--Chris