Slaten will be 32 in February and could actually prove to be pretty useful if used correctly. Over his career, he has held lefties to a .241/.304/.361 line. His numbers against righties, however, are pretty awful. He pitched just 16 1/3 innings last year for Washington due to an elbow injury.
He will compete for a job in the bullpen, but I would say he is a bit of a long shot to make the club out of Spring Training.