Almost certainly not. There's almost no reason someone would be playing corner OF (and stuck in AAAA purgatory for years) if there were even a reasonable probability that he could play 3B. You can switch from infield to outfield fairly easily. It's hard to remember someone doing the reverse.
Note the hinge: Carter Kieboom has never shown a hint that he is a major league ballplayer. It's time for the Nats to admit that and make some provision. Castro belongs at 2B/ He can play third, but that pulls Harrison from being a good utility guy. Someone has to play third and hit.
Incidentally, Killebrew was and outfielder until a AAA coach from the White Sox suggested he get closer to the plate. With that, Killebrew came to spring training in 1959 and hit homers. The Nats were desperate, so they never took the time to teach him to field -- they had traded Eddie Yost to Detroit, so there was a spot. The New Nats let Anthony Rendon sign with LA, so there is a hole at third.
