They would get along great (depending on their personalities, of course). I lived next door to my uncle as a teenager; we had a GSD and he had a Dobe. We took the fence down between the yards so they could play any time they wanted - Lucky and Roxy were BFF's! They had the same level of drive and were about the same size so it worked well. Before I got Ralphie, I was looking at possibly adopting an albino Doberman and if husband ever agrees to a second dog, I planned on it being a Dobe!
Ralphie - GSD (mix??), rescue
Nightshade - born 6/1/2003 - Domestic medium hair/Maine Coon mix (feline)
James - Domestic short hair (feline), rescue