Hi mike,
I use 8 RGB Led with common anode with my dlc-247 for RPM and other data (8 physical leds = 24 lights) and everything works well, i don't know if in iRacing the flag data come to be displayed but in other sim works perfectly.
The SMD RGB LED you have linked seem to haven't a common anode but they should work fine so you need to wire like a simple monocolor led.
You need to wire the led pin 6, 7, 8, to pin 17 of dlc-247 and the pin 1, 2, 3, to the dlc-247 pin 1, 2, 3.