The issue is particularly vexing since Samsung is usually quite good about releasing open-source code for its devices. And indeed, the Vibrant’s code is available, but the specific bit of code required for full access to the wireless radio is not. Samsung has a pretty good relationship with the modder community, especially after hiring Steve “Cyanogen” Kondik. I’ve got to believe that Mr. Kondik tried to get the relevant data from his employers, to no avail.
The CM team has dropped support for devices before when they hit a way that would make satisfactory development impossible. It’s likely that more modders will take CyanogenMod’s open source code and port it back to the Vibrant, but I wouldn’t recommend using it. You might never need to dial 911 from your cell phone, but going without the functionality is just asking for trouble. The Vibrant’s stock firmware was updated to Gingerbread, so it might be best to stick with that until you get a new phone, as the ROM developers suggest.
Here’s an odd one: the CyanogenMod team, makers of the most widely-used custom ROM out there, have completely dropped support for the T-Mobile Galaxy S Vibrant. It’s not a hardware issue, as CyanogenMod supports much older and weaker phones. No, the problem comes from Samsung’s proprietary radio software, which is apparently keeping the custom version of Android from dialing 911.