What do I need to know about the "weird" Galaxy S Vibrant emergency call handling?
The official announcement on the CM forums states:


The issue was in the RIL code, which is just typical code and libraries packaged in the ROM (e.g. /system/lib/libril.so, for example). The CM team recommended installing a Samsung ROM noting that any Samsung ROM is fine and any AOSP ROM would have issues. There's no permanent damage since the RIL code was replaced when you reflashed.
They specifically cited the issue was related to closed-source RIL code, so this wouldn't happen with a stock ROM unless Samsung severely borked their RIL code.
Only 911 was listed as a problem, but I don't know (and neither have the CM team ever stated) if other emergency numbers were affected.
Official support for the Vibrant didn't occur until 7.1, which was Gingerbread. It's really hard to say if older versions were affected, but I would assume yes (if they exist somewhere still).
The announcement states that the issue was fixed and the Vibrant is officially supported at this point.