Reducing voltages with LEDs or diodes is a common and cheap practice with some serious risks: since they subtract a fixed voltage, all dirt and spikes (you wrote you are driving motors, thus on 6V, you risk to have spikes up to 12V) will come through, also only lowered by that 1.x V which are eaten by the diode(s). That’s why I’d rather consider a low drop voltage regulator in a SOT23 housing which does not eat more space than a LED. Intelligent routing provided, you might operate that LDO regulator even without additional capacitors since the Teensy has already oneon the 5V side and your 6V are decoupled, too, I guess. If you can manage to keep PCB traces below 2 or 3cm from existing cap to ldo and ldo to existing cap, you should be fine.