Can a ideal black body be model of real Vacuum T= 0K ?

A blackbody at 0K has the same electromagnetic properties as a vac---absorbs everything sent to it, sends nothing back aside from vacuum fluctuations. So I suppose the answer to your question is "yes", sort of. But a physical blackbody at 0K will produce a different Casimir effect, I imagine. In other words, a conducting plate brought near a blackbody would have a different Casimir-effect force on it than a conducting plate adjacent to a vac.