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It seems that peverify.exe is a front-end to c:\Windows\Microsoft.NET\Framework\v4.0.30319\peverify.dll (or c:\Windows\Microsoft.NET\Framework\v2.0.50727\peverify.dll for CLR 2.0), which is a native DLL (actually, peverify.exe is also native)
I don't see this documented anywhere so it's probably not a public API. You may be able to figure out the exported functions from that DLL using something like Dependency Walker, but I think it would be simpler to just call peverify.exe.
EDIT: anecdotal evidence: