System Information (formerly known as System Profiler) will show you some information about the built-in camera (which Apple calls the iSight), but I don't see frame rate, exposure time, or shutter speed mentioned here. In my specific case, the manufacturer is listed as Apple, and they likely don't want to publish this information. Apple treats the built-in iSight as a simple checkbox feature (a computer has it or it doesn't), not as a detailed specs feature (like memory size, hard drive size, screen size, network speed, etc).
To view the information available about your Mac's built-in iSight, go to the Apple menu, choose About This Mac, then choose System Report… . From there, go into the Hardware section, choose USB, and look in the USB Device Tree for Built-in iSight.
iFixit is a company that often disassembles Apple products to try to determine things like the cost of the bill of materials, specific parts used, and unadvertised specs or capabilities of the hardware. You could visit their site and see if your machine is covered there, or if there's another way to get information about your machine.
The simple answer is no - in general the one camera only sends data to one app.
The more complicated answer is that the API (application programming interface) that Apple publishes enforces this restriction. If a developer hooks into the hardware directly or there is a bug in the API, it is possible to share that stream.
So for most Apps made by someone other than Apple, once the iSight is in use by one application, it is unavailable to other applications until the application releases the use of it or the application closes. User Gentmatt rightly points out that this is not the case for Facetime and Photobooth, where Apple is either using an undocumented or private API or accessing the hardware directly so that both apps can share the camera feed.
Best Answer
KeyLemon looks like what you want: http://www.keylemon.com/product/
It has a free version, but I don't believe it will replace the login screen.