For some context, DWAR is set against a league average. The base is rooted in UZR or DRS (depending on the source), and both of these numbers trend towards being cumulative. Long story short, limited playing time can negatively impact a players dWAR, which does make sense. No one adds defensive help from the bench.
For the Sox, this does mean part time players like Arroyo and Valdez would and should struggle to have positive defensive WAR contributions just due to playing time and regardless of fielding ability…