Are all DUB cranks compatible? I have a dub crankset with arm length 175 (< I want to change the crank arm length to 167.5 There's no 167.5 crank arm for SRAM MTB line (I think SX/NX/GX/XX1/X01 are MTBs?) I found `Red` and `Force` 167.5 arms which are also `DUB` (I think these `Red` and `Force` are for road?) So can I mix the `Red` or `Force` crank arm ( with my existing MTB crankset ?

Road cranks are not going to work on your MTB.

The crank arms include the crank axle - one of the arms is permanently attached to the axle. The axle length is important. Road bikes use narrower bottom bracket shells than MTBs and hence have shorter axles.