Can a MacBook's Thunderbolt port be used as an HDMI "in" to view a feed/signal from a video camera? I am a filmmaker who wants to be able to use my macbook as an external monitor for a video camera in a studio-interview type setting. The camera is decent, but its screen is small and I don't have any external monitors handy (money is tight). Is there some software that would be able to receive an HDMI-out signal from my camera and then display it on the macbook screen via an HDMI → Thunderbolt adaptor (I have one)?

So the flow would look like this: 

Camera → HDMI Cord → HDMI-to-ThBt Adaptor → Software to look at what the camera is sending → my eyes. 

Recording the feed is not necessary.
No, not directly.  You can buy any number of HDMI capture hardware that connect via thunderbolt or FireWire and use a thunderbolt FireWire adapter.