Your question unfortunately is a "given all apples are fruit, how can I verify that the specific piece of fruit I am holding is also an apple?"... it's not an easy question to answer... unless you have a lab full of equipment to test the genome of the fruit before you... or purchased it from a reputable dealer and it came pre-certified as an apple.
CIM is the base protocol.
WBEM is a specification, based on CIM which lays out some additional specifics.
SMI-S is another spec, based on WBEM and laying out a number of additional specifics.
So from the start, OpenPegasus & OpenWBEM are not automatically SMI-S compatible... only through the creation of SMI-S compatible profiles & providers are they can be.
When it comes to determine if a SMI-S provider/api/etc is actually compliant with the specs, that depends on what your requirements are and how much time & money you have to invest.
Like many protocols, it can sometimes be enough to simply see if it works well enough for your purposes and test with different configurations from different vendors along the way... one way to do that is to attend a SNIA plugfest: http://www.snia.org/forums/smi/tech_programs/lab_program
Given that SNIA owns the SMI-S standard, they also have a program for verifying compliance with it: http://www.snia.org/ctp/ (though it like many standard based verification will cost some $$$).