I have cruised HAL to Alaska and they did use boarding groups and were strict.
I have cruised RCCL to the Med in Barcelona and they were using boarding groups and were strict.
I have cruised fathom out of Miami twice and they have used boarding cards (from Carnival as they are under the Carnival umbrella and on a P&O ship (a line I will NEVER cruise again - P&O that is...fathom 2.0 pending their ship used) and were super strict.
So no,
DCL is not the only line that is strict about boarding groups.