Unfortunately, there's no such thing as SAML 2 compliant so it's a hard one to prove - although the conformance spec does say metadata is part of the standard.
There is the Interoperable SAML 2.0 Profile though. See it at http://saml2int.org/
It's a minimum set of profiles/bindings that I've used (as part of a significantly sized SAML service and software providing company) in the past for this purpose. It defines metadata requirements here: http://saml2int.org/profile/current#section5