/dev/dsp device comes from the old Open Sound System drivers, which are deprecated these days. The devices you've listed support the newer ALSA API, so can't be used with ffmpeg's
Instead follow the instructions in the other question, but modify the command to:
ffmpeg -f alsa -i $ALSA_DEVICE_NAME ...
$ALSA_DEVICE_NAME is the device name displayed by
arecord -L that corresponds to your webcam. It will likely list a few options for the webcam, but picking the one starting with
plughw: should be fine.