Do I have to use the Motorola reccomended Routers for MOTOTRBO?

The short answer is no.

The longer answer is that Motorola has validated a few Routers for use with MOTOTRBO systems and you can use whatever you like BUT if something doesnt work as it should, you'd have some difficultes getting support especially if the root cause is in the Router.
You should never use consumer grade Routers - they may more or less work but, from my experience, they introduce more problems than the saving you might make.

For IPSC and Capacity Plus, the validated Routers are the D-Link EBR-2310*; Linksys RVS4000* and HPE MSR2003AC. I and others have also used the Mikrotik RB2011 and the results have been good.
(*I dont have personal experience with these two models but they are mentioned in the System Planner.)

For Capacity Max, the validated Routers are the HPE MSR2003AC and the Cisco 2911. The benefit of using these two models is that there are example configuration files available on Motorola Online that you can load into the Routers, if you want to use the suggested IP plan. Again, you dont need to use either and you dont have to use the IP plan shown in the example config files.

Capacity Max normally also uses an Ethernet Switch: the two models that are listed are the HPE 2530-24 and Cisco 3650. For smaller RF Sites, there is a SIC module available for the HPE MSR2003AC that gives it another four ethernet ports which will save you from having to add in the abovementioned switch.

The HPE MSR2003AC is the sucessor to the MSR20-20.

What do you use? How did it go?