I didn’t get reports about incompatibility issues between URE and MUM yet.
With User Role Editor Pro you can follow this scenario:
1) add new user to the main site.
2) grant needed roles to this user.
3) open this user capabilities under the ‘Network admin -> Users -> All users’
You will see permissions which granted to him for the main site
Click “Update Network” button to add this user with the same roles and capabilities to all the rest subsites of your multisite network.
Roles and capabilities should exist at subsite in order to be granted to the new added user.
Use ‘Network admin -> Users -> User Role Editor -> Update Network’ to replicate all roles and capabilities from the main site to all the rest subsites of the network.
I think that following a scenario above you can do the same work as a MUM plugin offers according the quote you noted.
