There's plenty of reasons as to why the two point guards can co-exist.
In today's NBA, teams are gravitating towards small ball, as shown by the Golden State Warriors in the NBA Finals, who were able to get away with starting a 6-foot-7 Draymond Green at center on the far taller Timofey Mozgov. The reason? The NBA is getting quicker, with "pace and space" being the new mantra. In that regard, a pairing of Brandon Jennings and Reggie Jackson could be viewed as desirable. Both possess tremendous athleticism, with Jennings having elite speed and agility and Jackson with great strength, acceleration and body control.