The other way of communication of your javaservlet and webmethodsEnterprise is your servlet application can use Enterprise server brokerhost and broker name of your WMenterprise server and for this the servlet has to subscribe to your brokerclient so that enterprise can publish the events.
Regarding SOAP protocol i am not sure this will work out but this is the alternate of using protocols.

And we are using this procedure publish/subscribe to our internal application .we have b2b-enterprise-internal target application.

Hope you like this advice..