Would a bad alternator cause headlight flicker?

If you actually did what you said, you can NOT check these with an ohmeter. You must check voltage drop. The proof of whether or not the VR set point is "on target" is "what is?" the running voltage between the VR IGN terminal and the VR mounting flange?

With the engine warm and running "low to med cruise" RPM, if that voltage is within the set point recommendations (for me that boils down, no pun, to 13.8--14.2 warm) then regardless of what the battery is doing, then the VR is doing it's job.........regulating voltage at it's input terminal to that setpoint

The problem with actually CHECKING this is that EG the 70/ later cars, you cannot easily access the VR ign terminal, without, say, using gater clips or build some adapter, etc, or just clip to the ballast "key side" and use that

So far as automotive resistance checks "in general" the higher the amperage the circuit, the less resistance checks are reliable. Not only must the reading be incredibly accurate, and isn't, but you must be able to connect with the probes "solidly" in such a way that the probes themselves don't affect the reading, and last, some "problem" connections can CHANGE with amperage, leading you down the primrose lane.