Clarizen's SOAP API uses standard XML Web services. The WSDL can be retrieved from https://api2.clarizen.com/v1.0/clarizen.svc?wsdl
The end point for the SOAP API is https://api2.clarizen.com/v1.0/clarizen.svc. You can issue a GetServerDefinition call to get the final endpoint, though for now new customers are supposed to be using that address anyway. Anyway, The endpoint address is not supposed to change often.
As far as I know Boomi supports XML web services, though I don't know how well it handles the class inheritance Clarizen's service uses, and the login sequence.
We also have a REST API out there, but we're still constructing the documentation and samples.
I'd suggest you setup a .NET development environment if you can, because it's very easy to setup and test Clarizen's API with. When you've managed to get what you want with .NET you can try to port it into Boomi. It may prove to be less time consuming (but that's coming from someone who's fluent with .NET and has little knowledge of Boomi )
Hope this helps