Resistors generally serve two purposes.
They put a small additional load on the circuit to ensure the "circuit and lamp good" functions work.
But also LEDs are unlikely to be powered directly from the supplied voltage and will have some form of power supply, in some designs the small monitoring pulses can cause the power supply to charge enough to make the led briefly flash and flicker and the resistors can help with this. You can see this effect sometimes on a factory LED unit, several folks with a fully LED 6.1 report they can sometimes see a very dull glow from things like reverse lights until the van ECUs fully shut down.
Some designs need a balanced (identical) resistor on both left and right as they use the measured difference between two broadly identical circuits to tell if there is an issue, others monitor each circuit individually. I'm not sure what the T6/T6.1 does here. The balanced approach is the older design as it can be done quite simply with analogue electronics.
OEM units have the advantage they know precisely how the van ECUs will drive them so their power supply will be designed to work with that using whatever electronic design is best for the unit. For complex lights like the OEM headlights I believe all the control electronics are built into the unit so they are just supplied permanent 12v and communicate with the main ECU by canbus - so the van tells them which lights should be on and the unit can report any faults.
Indicators are a special case because of history. Original indicator flasher units used a bimetallic strip that heated up and cooled down and clicked on and off the circuit. A side effect of the design was if they didn't have enough load (both front and rear lamps) they clicked on and off too fast, but this turned out to be useful as it was an obvious way to alert the driver to a blown indicator lamp. So many modern electronics simulate this as many drivers are used to it. (They also simulate the flasher click as well as that's a useful reminder they are on - it's either done though the audio head unit or there is a "fake" actual relay on the dashboard electronics that click away - the clue is if you put the hazards on with ignition off there is no noise)
Personally I'd try and ensure the monitoring works rather than coding it out, it's not just checking the lamp it's checking the integrity of the whole circuit so will pick up wiring faults too.
