convert level to 12V to remotely drive WS2812 string

My scope shows only about 2. volts for the highs on the data string, is this normal? Figured that might be with the speed.

A normal opto-isolator (like the 4N25) is open-collector and it relies on the pull-up resistor for the positive output. Unless there is something "weird" about the load pulling-down against the pull-up, you should be getting darn-near 5V.

Try it at DC to see if it's related to switching speed.