What happend when router is stopped, and motors are not powered?! It's possible that someone to pull a belt (just to see if it moves, or by mistake etc.). I think that you will not have 90degree between X and Y axis - not good al all.
you could synchronize both motors at the start of work (solution are many), but how repetable is that?
It's no need for synchronization during work, if motors are "always ON" (Kcam and others can power-off stepper if it's not used for 5sec for example - you don't want this to happend). Both steppers/servo could be commanded with the same signals, and this way it will be synchronized.