What Moodle web service do you want to consume?
Do you just want to READ Moodle data, or do you want to perform WRITE operations too?
When the business system requires a Moodle validation it sends a request to BizTalk using a Moodle custom profile field value as the business identifier and BizTalk executes the Moodle stored procedure. BizTalk then receives the Moodle data as xml and forwards it on the the business system.
Not perfect... but it's worked for 3 years at approximately 6000 transactions per day. The client has a silly aversion to anything non-Microsoft, so for now it's ok.