I have lashed two locos, both DCC, and do so all of the time with A-B, A-A, A-B-B, even A-B-B-A and even ran two Big Boys in order to get a 200-car consist up a hill at a train show, one at the head and one "pushing". Almost all of my engines are DCC with just a few waiting to be converted.
But. pre-DCC, I would lash two engines, not even think of any problems. What did we do BEFORE DCC?